KERR MCGEE CORP /DE

election_required = True...hase all shares tendered by all holders of "odd lots" (as defined below) who: (1)properly tender all shares owned beneficially or of record at a price at or below the purchase price selected by us (partial tenders will not qualify for this preference); and (2)complete the section entitled "Odd Lots" in the Letter of Transmittal and, if applicable, in the Notice of Guaranteed Delivery; •second, we will purchase all other shares properly tendered and not properly withdrawn before the expiration of the tender offer, at prices at or below the purchase price selected by us on a pro rata basis (except for shares tendered subject to the condition that a specified mini...

expiry = 2005-05-18...on Stock (Including the Associated Preferred Stock Purchase Rights) at A Purchase Price Not Greater Than $92.00 Nor Less Than $85.00 Per Share THE TENDER OFFER, PRORATION PERIOD AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00 MIDNIGHT, NEW YORK CITY TIME, ON MAY 18, 2005, UNLESS THE TENDER OFFER IS EXTENDED. Kerr-McGee Corporation, a Delaware corporation ("Kerr-McGee"), invites its stockholders to tender up to 43,500,000 shares of its common stock, par value $1.00 per share, for purchase by us at a price n...

expiry = 2005-05-18...cluding the Associated Preferred Stock Purchase Rights) at A Purchase Price Not Greater Than $92.00 Nor Less Than $85.00 Per Share May 2, 2005 THE TENDER OFFER, PRORATION PERIOD AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00 MIDNIGHT, NEW YORK CITY TIME, ON MAY 18, 2005, UNLESS THE TENDER OFFER IS EXTENDED. Kerr-McGee Corporation, a Delaware corporation ("Kerr-McGee"), hereby amends and supplements its offer to purchase for cash up to 43,500,000 shares of its common stock, par value $1.00 per share, for p...

listed = True...in Section 9, and otherwise satisfactory to us, that will be sufficient to purchase shares tendered pursuant to the tender offer, refinance certain of our existing indebtedness and pay related fees and expenses. See Sections 7 and 9. Our shares are listed and traded on the New York Stock Exchange (the "NYSE") under the trading symbol "KMG". On April 13, 2005, the last full trading day before the announcement of the tender offer, the last reported sale price of the shares was $73.97 per share. You are urged to obtain current market quotations for the shares before deciding whether to tender your shares. See Section 8. OUR BOARD OF DIRECTORS...

mechanism = DUTCH...s of this Offer to Purchase where you will find a more complete discussion. Who is offering to purchase my shares? Kerr-McGee Corporation. What will be the purchase price for the shares? We are conducting the tender offer through a procedure commonly called a modified "Dutch Auction". This procedure allows you to select the price (in increments of $0.25) within a price range specified by us at which you are willing to sell your shares. The price range for this offer is $85.00 to $92.00 per share. The purchase price will be the lowest price at which, based on the number of shares tendered and the prices specified by...

mechanism = DUTCH...es to be Tendered (The total of all percentages must be less than or equal to 100%. If the total is less than 100%, you will be deemed to have directed Mourant ECS Trustees Limited NOT to tender the remaining percentage.) % Shares Tendered at Price Determined by Dutch Auction (By entering a percentage on the line above, the undersigned is willing to accept the Purchase Price resulting from the Dutch Auction, for the percentage of shares elected. This could result in receiving a price per share as low as $85.00 or as high as $92.00 per share.) OR % at $85.00 % at $86.50 % at $88.00 % at $89.50 % at $91.00 % at...

mechanism = FIXED...hares conditionally as provided in Section 6 of the Offer to Purchase, as amended and supplemented by this Supplement. Our intent is to purchase up to $4 billion of our shares in the tender offer. In the event the final purchase price is less than the maximum purchase price of $92.00 per share and more than 43,500,000 shares are tendered in the tender offer at or below the purchase price, we intend to exercise our right to purchase up to an additional 2% of our outstanding shares without extending the tender offer, so that we repurchase up to $4 billion of our shares. By way of example, if the final purchase price is the minim...

must_tender_all = True...from Kerr-McGee Corporation Savings Investment Plan Trustees," sent to them separately. See Section 4. In what order will you purchase the tendered shares? We will purchase shares: •first, from all holders of "odd lots" (persons who own fewer than 100 shares) who properly tender all of their shares at or below the purchase price selected by us and who do not properly withdraw them before the expiration of the tender offer; •second, on a pro rata basis from all other stockholders who properly tender shares at or below the purchase price selected by us and who do not properly withdraw them before the expiration of the tender offer, o...

must_tender_all = True...amended and supplemented by this Supplement, all of the shares tendered at or below the purchase price may not be purchased if more than the number of shares we seek are properly tendered. Prior to amending the tender offer, holders of "odd lots" who properly tendered all of their shares in the tender offer would have had priority over all other tendering stockholders with respect to proration. Following the amendment of the tender offer and except for those stockholders tendering their shares conditionally as provided in Section 6 of the Offer to Purchase, as amended and supplemented by this Supplement, all tendering st...

price = USD 85.0-92.0...fied "Dutch Auction". This procedure allows you to select the price (in increments of $0.25) within a price range specified by us at which you are willing to sell your shares. The price range for this offer is $85.00 to $92.00 per share. The purchase price will be the lowest price at which, based on the number of shares tendered and the prices specified by the tendering stockholders, we can purchase 43,500,000 shares, or such lesser number of...

price = USD 92.0...piration of the tender offer. Kerr-McGee's intent is to purchase up to $4 billion of its shares in the tender offer. In the event the final purchase price is less than the maximum purchase price of $92.00 per share and more than 43,500,000 shares are tendered in the tender offer at or below the purchase price, Kerr-McGee intends to exercise its right to purchase up to an additional 2% of its outstanding shares without extending th...

price = USD 92.0...d and supplemented by this Supplement. Our intent is to purchase up to $4 billion of our shares in the tender offer. In the event the final purchase price is less than the maximum purchase price of $92.00 per share and more than 43,500,000 shares are tendered in the tender offer at or below the purchase price, we intend to exercise our right to purchase up to an additional 2% of our outstanding shares without extending the tender...

priority = True...sh to withdraw their shares must follow the instructions found in the "Letter from Kerr-McGee Corporation Savings Investment Plan Trustees," sent to them separately. See Section 4. In what order will you purchase the tendered shares? We will purchase shares: •first, from all holders of "odd lots" (persons who own fewer than 100 shares) who properly tender all of their shares at or below the purchase price selected by us and who do not properly withdraw them before the expiration of the tender offer; •second, on a pro rata basis from all other stockholders who properly tender shares at or below the purchase price selected by us and who do not properly withdraw t...

threshold = 100...drawn. The 43,500,000 shares represent approximately 27.0% of our outstanding common stock as of March 31, 2005. If more than 43,500,000 shares are tendered, all shares tendered at or below the purchase price will be purchased on a pro rata basis, except for "odd lots" (lots held by owners of fewer than 100 shares), which will be purchased on a priority basis. The tender offer is not conditioned on any minimum number of shares being tendered. See Section 7. Our intent is to purchase up to $4 billion of our shares in the tender offer. In the event the final purchase price is less than the maximum price of $92.00 per share and more than 43,500,000 s...

threshold = 100...h together, as they may be further amended or supplemented from time to time, constitute the "tender offer"), to eliminate the priority for holders of "odd lots" with respect to proration that was initially contemplated in the tender offer. A person holds an "odd lot" when he or she owns fewer than 100 shares. We will select the lowest purchase price that will allow us to purchase 43,500,000 shares or, if a lesser number of shares are properly tendered, all shares that are properly tendered and not withdrawn. All shares acquired in the tender offer will be acquired at the same purchase price regardless of whether the stockholder tendered at a...

threshold = 100...elf-tender offer being made by Kerr-McGee Corporation. Enclosed is a Supplement to the Offer to Purchase previously sent to you that was prepared by Kerr-McGee Corporation. The Supplement amends the Offer to Purchase and eliminates the priority for holders of fewer than 100 shares ("odd lots") with respect to proration that was initially contemplated in the tender offer. The odd lot priority provided for in the original Offer to Purchase never applied to shares held in the Savings Investment Plan. As you may be aware, there will be a "freeze period" for the Savings Investment Plan during which you will be unable to process...

txn_type = TENDER_OFFEREX-99.1 2 a2155892zex-99_1.htm EXHIBIT 99.1 QuickLinks -- Click here to rapidly navigate through this document Exhibit (a)(1)(i) Offer to Purchase for Cash by Kerr-McGee Corporation of Up to 43,500,000 Shares of Its Common Stock (Including the Associated Preferred Stock Purchase Rights) at A Purchase Price Not Greater Than $92.00 Nor Less Than $85.00 Per Share THE TENDER OFFER, PRORATION PERIOD AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00 MIDNIGHT, NEW YORK CITY TIME, ON MAY 18, 2005...

txn_type = TENDER_OFFER...e tender offer, if feasible. The remainder of this letter summarizes the transaction, your rights under the Plan and the procedures for completing and submitting the enclosed Direction Form. You should also review the more detailed explanation provided in the Offer to Purchase, dated April 18, 2005 (the "Offer to Purchase") enclosed with this letter. You should note that your position may be different in some respects if you have ceased employment with a relevant Kerr McGee company. This is explained further in "Ceasing Employment" below. BACKGROUND Kerr-McGee Corporation, a Delaware corporation ("Kerr-McGee")...

txn_type = TENDER_OFFEREX-99.(A)(1)(X) 2 a2157303zex-99_a1x.htm EX 99(A)(1)(X) QuickLinks -- Click here to rapidly navigate through this document Exhibit (a)(1)(x) Supplement to the Offer to Purchase for Cash by Kerr-McGee Corporation of Up to 43,500,000 Shares of Its Common Stock (Including the Associated Preferred Stock Purchase Rights) at A Purchase Price Not Greater Than $92.00 Nor Less Than $85.00 Per Share May 2, 2005 THE TENDER OFFER, PRORATION PERIOD AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00 MIDNIGHT, NEW YORK CITY TIME, ON...

txn_type = TENDER_OFFEREX-99.(A)(1)(XV) 2 a2157482zex-99_a1xv.htm EX 99(A)(1)(XV) Exhibit (a)(1)(xv) Dear Plan Participant: We previously sent to you an Offer to Purchase, dated April 18, 2005, and certain other materials for your use in connection with a self-tender offer being made by Kerr-McGee Corporation. Enclosed is a Supplement to the Offer to Purchase previously sent to you that was prepared by Kerr-McGee Corporation. The Supplement amends the Offer to Purchase and eliminates the priority for hold...