SUMMARY

This brief summary highlights selected information from this prospectus. It does not contain all of the information that is important to CSK stockholders. CSK stockholders are urged to read carefully the entire prospectus and the other documents referred to and incorporated by reference in this prospectus to fully understand the offer and the merger. In particular, stockholders of CSK should read the documents attached to this prospectus, including the merger agreement, which is attached as Annex A. For a guide as to where you can obtain more information on O’Reilly, see “Additional Information—Where You Can Find Additional Information” on page 81.

The Offer

We are proposing to acquire all of the outstanding shares of CSK common stock in exchange for shares of O’Reilly common stock and cash.

Stock Component. The stock component consists of between 0.3673 and 0.4285 of a fully paid and nonassessable share of common stock, par value of $0.01, of O’Reilly as determined based on an “exchange ratio” equal to (i) $11.00 divided by (ii) the average of the reported closing sale prices of O’Reilly common stock for the five (5) consecutive trading days ending on and including the second trading day prior to the consummation of the exchange offer and rounded to four decimal places; provided, however, that if such average closing sale price of O’Reilly stock is greater than $29.95, then the exchange ratio shall equal 0.3673, and if such average closing sale price is less than $25.67, then the exchange ratio shall equal 0.4285.

Cash Component. The cash component consists of $1.00 in cash minus the adjustment amount, if any, which we refer to as the per share cash consideration. The adjustment amount is the amount equal to the quotient obtained by dividing (i) the sum of any amount paid by CSK or its subsidiaries to the lenders under its credit agreements in connection with obtaining any bank consent, waiver or amendment under the credit agreements after April 1, 2008 minus $3,000,000 by (ii) the sum of the (a) total number of shares of CSK common stock outstanding immediately prior to the expiration of the offer and (b) total number of shares of CSK common stock determined by O’Reilly up to a maximum of the total number of shares of CSK common stock issuable upon the exercise or conversion of all options, warrants, rights and convertible securities (if any) that will be vested by September 28, 2008. The adjustment amount will be rounded down to the nearest 1/10 (one-tenth) of a cent and will in no event be greater than $1.00 or less than zero. CSK has indicated to O’Reilly that, as of the date of this prospectus, it does not anticipate obtaining any bank consent, waiver or amendment under its credit agreements prior to the anticipated completion of the offer.

After completion of the offer, O’Reilly will cause OC Acquisition to complete a merger with and into CSK in which each outstanding share of CSK common stock (except for shares beneficially owned directly or indirectly by O’Reilly for its own account and any shares held in treasury by CSK) will be converted into the right to receive the same consideration paid in exchange for each share of CSK common stock in the offer, subject to appraisal rights to the extent applicable under Delaware law. If, after the completion of the offer, either as a result of the offer alone or in conjunction with the exercise of our top-up option to purchase shares directly from CSK, we beneficially own more than 90% of the outstanding shares of CSK common stock, we may effect the merger without the approval of CSK stockholders, as permitted under Delaware law. If, on the other hand, after the completion of the offer, we beneficially own more than 50%, but less than 90%, of the outstanding shares of CSK common stock, a meeting of CSK stockholders and the affirmative vote of at least a majority of the shares of CSK common stock outstanding on the record date for such meeting will be needed to complete the merger. Since O’Reilly will own a majority of the shares of CSK common stock outstanding on the record date for any such meeting, approval of the merger by CSK stockholders will be assured.

The number of shares of O’Reilly common stock issued to CSK stockholders in the offer and the merger will constitute approximately 14.0% of the outstanding common stock of the combined company after the merger, based upon the number of outstanding shares of O’Reilly common stock and CSK common stock on June 17, 2008 and based on the average of the reported closing sale prices of O’Reilly common stock as reported on the NASDAQ for the five (5) consecutive trading days ending on and including June 17, 2008, disregarding stock options, and shares of common stock that may be issued by O’Reilly or CSK pursuant to an employee stock plan.

Exchange of Shares of CSK Common Stock (Page 33)

Upon the terms and subject to the conditions of the offer, promptly after the expiration of the offer, we will accept shares of CSK common stock that are validly tendered and not properly withdrawn in exchange for shares of O’Reilly common stock and cash. Each share of CSK common stock validly tendered and not properly withdrawn prior to the expiration of the offer will be exchanged for between 0.3673 and 0.4285 of a share of O’Reilly common stock and $1.00 in cash, subject to possible reduction, as described herein.

Timing of the Offer (Page 34)

We commenced the offer on June 11, 2008, the date of distribution of the initial prospectus. The offer is scheduled to expire at 12:00 midnight, New York City time, on July 10, 2008, unless we extend the period of the offer. All references to the expiration of the offer mean the time of expiration, as extended.

Conditions of the Offer (Page 35)

The offer is subject to a number of conditions, and O’Reilly will not be required to accept any tendered shares of CSK common stock for exchange if any of these conditions are not satisfied or, where permissible, waived as of the expiration of the offer. These conditions provide, among other things, that:

O’Reilly has agreed with CSK in the merger agreement that it will not consummate the offer unless the conditions set forth in the third, fourth, and fifth bullet points in the immediately preceding paragraph are

satisfied or waived by CSK. In addition, unless waived by CSK, O’Reilly has also agreed with CSK in the merger agreement that it will not consummate the offer if there shall have been any event having a material adverse effect on O’Reilly or any material breaches by O’Reilly of the merger agreement, in each case that have not been cured.

Extension, Termination and Amendment (Page 34)

In the event that the conditions to the offer have not been satisfied or waived upon the expiration of the offer (as the same may be extended), we are required to extend the offer for periods of up to twenty (20) business days until the earlier of such time that all of the conditions to the offer have been satisfied or waived or the merger agreement has been terminated in accordance with its terms. In addition, we, in our sole discretion, will extend the offer for an aggregate period of not more than ten (10) business days beyond the last expiration date of the offer that would otherwise be permitted if, in our reasonable discretion, such extension is necessary to complete the necessary conditions to complete our financing transactions for the offer so long as such extension does not extend the expiration date of the offer beyond thirty (30) business days following commencement of the offer. During any extension, all shares of CSK common stock previously tendered and not validly withdrawn will remain deposited with the exchange agent, subject to your right to withdraw your shares of CSK common stock. If we exercise our right to use a subsequent offering period as described below, we will first consummate the exchange with respect to the shares validly tendered and not properly withdrawn in the initial offer period.

In the event the merger agreement is terminated in accordance with its terms prior to the acceptance of any shares of CSK common stock for exchange pursuant to the offer, we will promptly terminate the offer without accepting any shares that were previously tendered.

Subsequent Offering Period (Page 35)

We may elect to provide subsequent offering periods of up to twenty (20) business days after the acceptance of shares of CSK common stock in the offer in accordance with Rule 14d-11 under the Exchange Act if, on the expiration date of the offer, all of the conditions to the offer have been satisfied or waived, but the total number of shares of CSK common stock that have been validly tendered and not withdrawn pursuant to the offer, together with shares of CSK common stock then directly or indirectly owned by O’Reilly, is less than 90% of the total number of shares of CSK common stock then outstanding. If we exercise our right to use a subsequent offering period, we will first consummate the exchange with respect to the shares validly tendered and not properly withdrawn in the initial offer period. You will not have the right to withdraw any shares of CSK common stock that you tender in the subsequent offering period. If we elect to provide a subsequent offering period, we will make a public announcement to that effect no later than 9:00 a.m. New York City time on the next business day after the previously scheduled expiration.

Procedure for Tendering Shares (Page 38)

For you to validly tender shares of CSK common stock pursuant to the offer, the enclosed letter of transmittal, properly completed and duly executed, or a manually executed facsimile of that document, along with any required signature guarantees, or an agent’s message in connection with a book-entry transfer, and any other required documents, must be transmitted to and received by the exchange agent at one of its addresses set forth on the back cover of this prospectus, and certificates for tendered shares of CSK common stock must be received by the exchange agent at one of its addresses or those shares of CSK common stock must be tendered pursuant to the procedures for book-entry tender set forth below, and a confirmation of receipt of the tender received, which confirmation we refer to below as a book-entry confirmation, in each case before the expiration date.

Guaranteed Delivery (Page 39)

If you wish to tender shares of CSK common stock pursuant to the offer and your certificates are not immediately available or you cannot deliver the certificates and all other required documents to the exchange agent prior to the expiration date or cannot complete the procedure for book-entry transfer on a timely basis, your shares of CSK common stock may nevertheless be tendered, if you comply with the guaranteed delivery procedures as set forth in “The Offer—Guaranteed Delivery” on page 39.

Withdrawal Rights (Page 40)

You may withdraw any shares of CSK common stock that you previously tendered into the offer at any time before the expiration of the offer by following the procedures described under “The Offer—Withdrawal Rights” on page 40.

Delivery of Shares of O’Reilly Common Stock and Cash (Page 42)

Subject to the satisfaction (or, where permissible, waiver) of the conditions to the offer as of the expiration of the offer, we will accept for exchange shares of CSK common stock validly tendered and not properly withdrawn promptly after the expiration of the offer and will exchange shares of O’Reilly common stock, $1.00 minus the adjustment amount, if any, and cash in lieu of fractional shares for the tendered shares of CSK common stock. In all cases, the exchange of shares of CSK common stock tendered and accepted for exchange pursuant to the offer will be made only if the exchange agent timely receives:

Cash Instead of Fractional Shares of O’Reilly Common Stock (Page 42)

We will not issue any fractional shares of O’Reilly common stock pursuant to the offer or the merger. Rather, O’Reilly will arrange for the exchange agent to make a cash payment in lieu of the fractional shares.

The Merger (Page 60)

The merger agreement provides that following completion of the offer OC Acquisition will be merged with and into CSK, with CSK continuing as the “surviving corporation.” In the event that O’Reilly beneficially owns more than 90% of the outstanding shares of CSK common stock upon completion of the offer, the merger agreement provides that the parties will take all necessary and appropriate action to cause the merger to become effective as soon as practicable following completion of the offer, without a meeting of CSK stockholders, by effecting a “short form” merger under Delaware law. If the minimum tender condition is met, we have the option, subject to certain limitations described herein, which we refer to as the top-up option, to purchase from CSK additional shares of common stock that, when added to the number of shares already owned by O’Reilly, will constitute one share more than 90% of the shares of CSK common stock then outstanding. If after the completion of the offer O’Reilly beneficially owns more than 50%, but less than 90%, of the outstanding shares of CSK common stock and O’Reilly’s exercise of the top-up option will not result in it owning one share more than 90% of the outstanding shares of CSK common stock, a meeting of CSK stockholders and the affirmative vote of at least a majority of the shares of CSK common stock outstanding on the record date for such meeting will be needed to complete the merger. Since O’Reilly will own a majority of the shares of CSK common stock

outstanding on the record date for any such meeting, approval of the merger by CSK stockholders will be assured. If necessary to preserve the intended treatment of the offer and the merger as a tax-free reorganization for United States federal income tax purposes, O’Reilly will cause the LLC merger to occur immediately after the merger.

No Solicitation of Acquisition Proposals (Page 63)

CSK has agreed, subject to limited exceptions, that neither CSK nor any of its subsidiaries nor any of their respective officers, directors, employees, agents and representatives will initiate or engage in any negotiations concerning an acquisition proposal. However, the merger agreement provides that, prior to the consummation of the offer, CSK may, in response to an unsolicited bona fide third-party acquisition proposal that CSK’s board determines in good faith (after consultation with CSK’s outside legal counsel and financial advisors) constitutes or may reasonably be expected to lead to a superior proposal:

CSK has also agreed to advise O’Reilly orally and in writing within forty-eight (48) hours of the receipt of any inquiries, proposals or offers regarding any acquisition proposal; any request for non-public information relating to CSK or its subsidiaries (other than requests for information not reasonably expected to be related to an acquisition proposal); and any inquiry or request for discussion or negotiation regarding an acquisition proposal.

Termination of the Merger Agreement (Page 68)

The merger agreement provides that it can be terminated by CSK or O’Reilly under a number of different scenarios, including:

Termination Fee (Page 69)

Termination of the merger by either O’Reilly or CSK under specified circumstances could result in CSK being required to pay O’Reilly a termination fee equal to $22 million. In the event that the merger agreement is terminated by O’Reilly because CSK files for bankruptcy or because of certain adverse events related to CSK’s failure to meet its existing debt obligations, CSK is obligated to pay O’Reilly for its actual documented reasonable out-of-pocket expenses in connection with the negotiation, execution and delivery of the merger agreement, compliance by O’Reilly with the merger agreement and actions taken in furtherance of the consummation of the transactions contemplated in the merger agreement.

CSK Board of Directors (Page 59)

The merger agreement provides that, upon acceptance for exchange of shares of CSK common stock in the offer, we will be entitled to designate a number of directors of CSK, rounded up to the next whole number, equal to the product of the total number of directors on CSK’s board of directors and the percentage of aggregate number of shares of CSK common stock beneficially owned by us. This would enable us to control the CSK board of directors after completion of the offer.

Material United States Federal Income Tax Considerations (Page 42)

It is a condition to the completion of the offer that O’Reilly and CSK receive written opinions from their respective tax counsel to the effect that the offer, the merger and the LLC merger (if any) together will constitute a reorganization within the meaning of section 368(a) of the Code. A CSK stockholder who, consistent with such opinions, receives cash (other than cash in lieu of a fractional share of O’Reilly common stock) and shares of O’Reilly common stock pursuant to a transaction constituting a reorganization within the meaning of section 368(a) of the Code will recognize gain (but will not recognize any loss), and the gain recognized will be equal to the lesser of (i) any cash received (other than cash received in lieu of a fractional share of O’Reilly common stock) and (ii) the excess, if any, of (x) the sum of the cash received (other than cash received in lieu of a fractional share of O’Reilly common stock) and the fair market value of the O’Reilly common stock received over (y) the CSK stockholder’s tax basis in the shares of CSK common stock exchanged therefor. In addition, the CSK stockholder will recognize gain or loss attributable to cash received in lieu of a fractional share of O’Reilly common stock. CSK stockholders should consult their tax advisors for a full understanding of all of the tax consequences of the offer, the merger and the LLC merger (if any) to them.

Appraisal Rights (Page 47)

Under Delaware law, you will not have any appraisal rights in connection with the offer. However, the merger is expected to entitle you to appraisal rights under Section 262 of the Delaware General Corporation Law, which we refer to as the DGCL. A copy of the appraisal rights provisions of the DGCL is attached as Annex B to this prospectus.

Regulatory Approvals (Page 47)

We and CSK have agreed pursuant to the merger agreement to use all reasonable best efforts to take whatever actions are required to obtain necessary regulatory approvals with respect to the offer and the merger. Other than clearance under the antitrust laws applicable to the offer and the merger, which are described below, the SEC declaring the effectiveness of the registration statement of which this prospectus is a part, and the filing of a certificate of merger under the DGCL with respect to the merger, we do not believe that any additional governmental filings are required with respect to the offer and the merger.

Under the HSR Act, and the related rules, the merger may not be completed until we and CSK notify and furnish information to the Federal Trade Commission and the Antitrust Division of the United States Department of Justice and specified waiting period requirements have been satisfied. The applicable waiting period under the HSR Act was terminated on April 17, 2008.

Financing of the Offer and the Merger (Page 49)

The offer is not conditioned upon the receipt of financing. O’Reilly estimates that the total amount of funds necessary to consummate the transactions contemplated by the offer and the merger will be approximately $1.2 billion, a substantial portion of which will be used to (i) refinance certain existing indebtedness of O’Reilly and CSK, (ii) pay customary fees and expenses relating to the offer, the merger and the financing, (iii) pay approximately $42.2 million to holders of CSK common stock for the cash portion of the offer consideration and (iv) provide for ongoing working capital requirements of the combined corporation. O’Reilly has received a commitment letter from Bank of America, N.A., Banc of America Securities LLC, Lehman Commercial Paper Inc., Lehman Brothers Commercial Bank and Lehman Brothers Inc. to provide an asset-based senior secured credit facility to provide $1.075 billion through a revolving credit facility and $125.0 million through a first-in-last-out revolving credit facility. See “Certain Effects of the Offer—Financing of the Offer and the Merger” starting on page 49 for more information.

Accounting Treatment (Page 50)

In accordance with Statement of Financial Accounting Standards (“SFAS”) No. 141, “Business Combinations,” O’Reilly will account for the transactions as a purchase business combination. Upon consummation of the transactions, O’Reilly will record the acquisition at cost with cost consisting of the fair value of O’Reilly common stock and stock options issued, the cash consideration issued and transaction costs. The total cost will be allocated based on the fair value of tangible and intangible assets acquired and liabilities assumed. The excess of cost over the fair value of net assets acquired will be recorded as goodwill.

Interests of Certain Persons in the Offer and the Merger (Page 52)

Certain CSK directors, officers and stockholders have interests in the offer and the merger that are different from, or are in addition to, those of other stockholders. These interests include:

The boards of directors of CSK and O’Reilly were aware of these interests and considered them, among other matters, when they approved the offer, the merger and the merger agreement.

As of the date of this prospectus, O’Reilly beneficially owns of record 2,153,928 shares of CSK common stock, constituting approximately 4.9% of the fully diluted shares of CSK common stock. Such shares will be counted for purposes of determining whether the minimum tender condition in the offer has been satisfied and, after completion of the offer, O’Reilly will vote such shares in favor of the merger.

Comparison of Rights of Holders of O’Reilly Common Stock and CSK Common Stock (Page 72)

CSK is a Delaware corporation, while O’Reilly is a Missouri corporation. If we complete the offer, holders of CSK common stock will become O’Reilly shareholders, and their rights as shareholders will be governed by Missouri law as well as O’Reilly’s articles of incorporation and bylaws. There are differences between Delaware law, the certificate of incorporation and bylaws of CSK, on the one hand, and Missouri law, the articles of incorporation and bylaws of O’Reilly, on the other hand.

The Companies

O’Reilly Automotive, Inc.

233 South Patterson

Springfield, Missouri 65802

Telephone: (417) 862-6708

www.oreillyauto.com

O’Reilly Automotive, Inc., founded in 1957 and incorporated under the laws of Missouri, is one of the largest specialty retailers of automotive aftermarket parts, tools, supplies, equipment and accessories in the United States. O’Reilly sells its products to do-it-yourself customers and professional installers. As of March 31, 2008, we operated 1,867 stores in Alabama, Arkansas, Florida, Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Minnesota, Mississippi, Missouri, Montana, Nebraska, North Carolina, North Dakota, Ohio, Oklahoma, South Carolina, South Dakota, Tennessee, Texas, Virginia, Wisconsin and Wyoming.

O’Reilly’s common stock is currently quoted on the NASDAQ (symbol: ORLY).

CSK Auto Corporation

645 E. Missouri Ave., Suite 400

Phoenix, Arizona 85012

Telephone: (602) 265-9200

www.cskauto.com

CSK Auto Corporation, founded in 1993 and incorporated under the laws of Delaware, is the largest specialty retailer of automotive parts and accessories in the Western United States and one of the largest such retailers of products in the country. As of May 4, 2008, through its wholly owned subsidiary, CSK Auto, Inc., CSK operated 1,345 stores in the United States, principally concentrated in the western United States. CSK’s stores are known by the following four brand names: (i) Checker Auto Parts, founded in 1969, with 487 stores in the Southwestern, Rocky Mountain and Northern Plains states and Hawaii; (ii) Schuck’s Auto Supply, founded in 1917, with 222 stores in the Pacific Northwest states and Alaska; (iii) Kragen Auto Parts, founded in 1947, with 504 stores primarily in California; and (iv) Murray’s Discount Auto Stores, founded in 1972, with 136 stores in the Midwest.

CSK’s common stock is currently quoted on the NYSE (symbol: CAO).

Comparative Per Share Market Price and Dividend Information (Page 18)

On March 31, 2008, the last trading day before O’Reilly and CSK announced the offer, O’Reilly common stock closed at $28.52 per share and CSK common stock closed at $9.31 per share. On June 17, 2008, the last

trading day prior to the printing of this prospectus for which this information was practicably available, O’Reilly common stock closed at $25.55 per share and CSK common stock closed at $11.50 per share.

Neither O’Reilly nor CSK has paid any dividends in the prior two fiscal years and O’Reilly does not anticipate paying any cash dividends on its common stock in the foreseeable future.

Questions About the Offer and Subsequent Merger

If you have any questions about the offer or the merger or if you need additional copies of this prospectus, you should contact our information agent:

INNISFREE M&A INCORPORATED

501 Madison Avenue, 20^th Floor

New York, NY 10022

Stockholders Call Toll-Free: (888) 750-5834

Banks and Brokers Call Collect: (212) 750-5833

SELECTED HISTORICAL FINANCIAL DATA

O’Reilly’s Selected Historical Consolidated Financial Data

The information in the following table is based on O’Reilly’s historical financial statements that O’Reilly has presented in its prior filings with the SEC. You should read the selected historical financial data in the following table in conjunction with the historical financial statements and related notes (including other selected historical financial data contained therein), O’Reilly’s “Management’s Discussion and Analysis of Financial Condition and Results of Operations” set forth in O’Reilly’s Annual Report on Form 10-K for the year ended December 31, 2007 and O’Reilly’s “Management’s Discussion and Analysis of Financial Condition and Results of Operations” set forth in O’Reilly’s Quarterly Report on Form 10-Q for the quarter ended March 31, 2008, which have been incorporated into this document by reference. See “Additional Information—Where You Can Find Additional Information” on page 81.

The historical consolidated financial data for O’Reilly for the fiscal years 2007, 2006, 2005, 2004 and 2003 have been derived from O’Reilly’s consolidated financial statements, which were audited by Ernst & Young LLP, an independent registered public accounting firm. The accompanying selected interim financial data for O’Reilly for the three months ended March 31, 2008 and 2007 have been derived from O’Reilly’s unaudited interim financial statements. The unaudited interim financial statements include all adjustments, consisting of normal recurring accruals, which O’Reilly considers necessary for a fair presentation of the financial position and the results of operations for these periods. Operating results for the three months ended March 31, 2008 are not necessarily indicative of the results that may be expected for the entire year ending December 31, 2008.

Amounts (except per share amounts) are shown in thousands.

CSK’s Selected Historical Consolidated Financial Data

The information in the following table is based on the historical financial statements of CSK included elsewhere in this prospectus. You should read the selected historical financial data in the following table in conjunction with the historical financial statements and related notes (including other selected historical financial data contained therein), CSK’s “Management’s Discussion and Analysis of Financial Condition and Results of Operations” set forth in CSK’s Annual Report on Form 10-K for the year ended February 3, 2008, attached as Annex D to this prospectus, and CSK’s “Management’s Discussion and Analysis of Financial Condition and Results of Operations” set forth in CSK’s Quarterly Report on Form 10-Q for the quarter ended May 4, 2008, attached as Annex G to this prospectus.

The historical consolidated financial data for the fiscal years 2007, 2006, 2005, 2004 and 2003 have been derived from the consolidated financial statements of CSK, which were audited by PricewaterhouseCoopers LLP, an independent registered public accounting firm. The accompanying selected interim financial data for CSK for the thirteen week periods ended May 4, 2008 and May 6, 2007 have been derived from CSK’s unaudited interim financial statements. The unaudited interim financial statements include all adjustments, consisting of normal recurring accruals, which CSK considers necessary for a fair presentation of the financial position and the results of operations for these periods. Operating results for the thirteen weeks ended May 4, 2008 are not necessarily indicative of the results that may be expected for the entire year ending February 1, 2009.

Amounts (except per share amounts) are shown in thousands.

SELECTED UNAUDITED PRO FORMA CONDENSED COMBINED FINANCIAL DATA

The following selected unaudited pro forma financial data is designed to show how the merger of O’Reilly and CSK might have affected the historical financial data of O’Reilly, giving effect to the merger and related financing as if they had been consummated at an earlier date. The following selected unaudited pro forma financial data gives effect to the merger and related financing as if they had been completed on March 31, 2008, with respect to the pro forma balance sheet data, and as of January 1, 2007, with respect to the pro forma statement of income data. The historical financial data has been adjusted to give effect to pro forma events that are directly attributable to the merger, factually supportable, and expected to have a continuing impact of the combined results.

The following unaudited pro forma condensed, combined financial data should be read in conjunction with the historical consolidated financial statements and notes thereto of O’Reilly, which are incorporated into this document by reference and the historical consolidated financial statements and notes thereto of CSK, which are set forth in CSK’s Annual Report on Form 10-K for the year ended February 3, 2008, attached as Annex D to this prospectus and CSK’s Quarterly Report on Form 10-Q for the quarter ended May 4, 2008, attached as Annex G to this prospectus. See “Additional Information—Where You Can Find Additional Information” on page 81. Certain amounts in CSK’s historical financial statements have been reclassified to conform to O’Reilly’s presentation of such items.

The following selected unaudited pro forma condensed combined financial data was prepared using the purchase method of accounting with O’Reilly treated as the acquiring entity and reflect adjustments, which are based upon preliminary estimates, to allocate the estimated purchase price to CSK’s assets acquired and liabilities assumed. For purposes of estimating the purchase price, it is assumed that the $1.00 in cash per share to be received by CSK stockholders will not be reduced. The purchase price allocation reflected herein is preliminary insofar as the final allocation will be based upon the actual purchase price and the actual assets acquired and liabilities assumed of CSK as of the date of the completion of the merger. The final allocation of the purchase price is also dependent upon certain required valuations and other analyses that cannot be completed prior to the merger. In certain instances, O’Reilly has identified intangible assets of CSK for which there has not been sufficient information available to make a preliminary estimate of fair value as of the date of this prospectus. For example, O’Reilly expects to record assets and liabilities for fair value adjustments to CSK lease arrangements once access to all of CSK’s lease information and market research is available to O’Reilly. The purchase price paid for these intangible assets has been allocated to goodwill until such time as a preliminary estimate is available. Additionally, we have not received sufficient information to make a preliminary estimate of the fair value of CSK’s inventory and property and equipment and the purchase price paid for these assets has been reflected in the pro forma data at CSK’s historical cost. Accordingly, the actual purchase accounting adjustments will differ from the preliminary pro forma adjustments reflected herein. See “Unaudited Pro Forma Condensed Combined Financial Data” on page 84 for additional details regarding these matters.

The following selected unaudited pro forma financial data are presented for illustrative purposes only and are not necessarily indicative of the financial condition or results of operations that actually would have been realized had the merger and related financing been completed on the dates indicated above. In addition, the following selected unaudited pro forma financial data does not purport to project the future financial condition or results of operations of the combined company. It should also be noted that O’Reilly and CSK have different fiscal year ends. Accordingly, the selected unaudited pro forma income statement data for the calendar year ended December 31, 2007 combines O’Reilly’s historical consolidated income statement data for the year then ended with CSK’s historical consolidated income statement data for the fiscal year (fifty-two (52) weeks) ended February 3, 2008. The selected unaudited pro forma income statement data for the three months ended March 31, 2008 combines O’Reilly’s historical consolidated income statement data for the three calendar months then ended with CSK’s historical consolidated income statement data for its first fiscal quarter (thirteen (13) weeks)

ended May 4, 2008. The selected unaudited pro forma balance sheet data combines O’Reilly’s historical consolidated balance sheet data as of March 31, 2008 with CSK’s historical consolidated balance sheet data as of May 4, 2008.

UNAUDITED COMPARATIVE PER COMMON SHARE DATA

The following table summarizes the net income from continuing operations and book value per common share information for O’Reilly and CSK on a historical and unaudited pro forma combined basis. The table accounts for the different fiscal years of O’Reilly and CSK discussed above in “Selected Unaudited Pro Forma Condensed Combined Financial Data.”

The pro forma book value combined per common share of O’Reilly is computed by dividing total pro forma shareholders’ equity by the pro forma number of shares of O’Reilly common stock outstanding at the end of the period, in each case, after giving effect to the merger and the related financing. The historical book value per common share of O’Reilly and CSK is computed by dividing total shareholders’ equity by the number of shares of common stock outstanding at the end of the period.

O’Reilly expects to incur merger and integration charges as a result of combining O’Reilly and CSK. O’Reilly also anticipates that the merger will provide the combined company with financial benefits that include reduced operating expenses and the opportunity to generate more revenue. The pro forma financial data, while helpful in illustrating the financial characteristics of the combined company under one set of assumptions, does not reflect these expenses or benefits and, accordingly, does not attempt to predict or suggest future results. It also does not necessarily reflect what the historical results of the combined company would have been had O’Reilly and CSK actually been combined during the periods presented.

The historical per share data of O’Reilly has been derived from, and should be read in conjunction with, the historical financial statements of O’Reilly incorporated by reference in this prospectus. See “Where You Can Find Additional Information” beginning on page 81. The historical per share data of CSK has been derived from, and should be read in conjunction with, the historical financial statements of CSK included elsewhere in this prospectus. See “Annex D – CSK’s Annual Report on Form 10-K for the year ended February 3, 2008” beginning on page D-1 and “Annex G – CSK’s Quarterly Report on Form 10-Q for the quarter ended May 4, 2008” beginning on page G-1. The unaudited pro forma per share data has been derived from, and should be read in conjunction with, the unaudited condensed combined pro forma financial statements included elsewhere in this prospectus. See “Unaudited Pro Forma Condensed Combined Financial Data” beginning on page 84.

The CSK unaudited pro forma combined equivalent share data was calculated by multiplying the corresponding O’Reilly unaudited pro forma combined per share data by an estimate of the exchange ratio of 0.4285, which is based upon the average of the reported closing sale prices of O’Reilly common stock for the five (5) consecutive trading days ending on and including June 17, 2008. This data shows how each share of CSK common stock would have participated in net income and book value of O’Reilly if the companies had been consolidated for accounting and financial reporting purposes for the periods presented. The equivalent earnings per share data does not give effect to the cash portion of the offer consideration. These amounts, however, are not intended to reflect future per share levels of net income and book value of O’Reilly.

COMPARATIVE PER SHARE MARKET PRICE AND DIVIDEND INFORMATION

O’Reilly common stock is listed on the NASDAQ, under the symbol “ORLY”. CSK common stock is listed on the NYSE under the symbol “CAO”. The table below sets forth, for the periods indicated and the range of high and low per share sales prices for O’Reilly common stock and CSK common stock as reported on the NASDAQ and NYSE, respectively. Neither O’Reilly nor CSK has paid any dividends for the calendar quarters indicated. For current price information, you should consult publicly available sources. For more information on O’Reilly’s payment of dividends, see “—O’Reilly’s Dividend Policy” below on this page.

O’Reilly and CSK have different fiscal years as discussed above in “Selected Unaudited Pro Forma Condensed Combined Financial Data.”

O’Reilly Common Stock

CSK Common Stock