MARATHON OIL CORPORATION 5555 San Felipe Road Houston, TX 77056-2723 Marathon Oil Corporation The United States Securities and Exchange Commission (SEC) permits oil and gas companies, in their filings with the SEC, to disclose only proved reserves. In this summary annual report wrap, we use certain terms to refer to reserves other than proved reserves, which the SEC’s 2005 Annual Report guidelines strictly prohibit us from including in filings with the SEC. These terms include reserves, resources and other similar terms, which are not yet classified as proved reserves. This summary annual report wrap also contains forward-looking statements about Marathon’s business including, but not limited to, the timing and levels of production, future exploration and drilling activity, reserve or resource additions, a plan for development and operation of the Alvheim and Vilje fields, an LNG project and possible expansion plans, the Neptune development, estimated levels and timing of production associated with the Company’s return to Libya, possible expansion of the Garyville, Louisiana, refinery and a $2 billion common stock repurchase program. The information related to reserve or resource additions is based on certain assumptions, including, among others, presently known physical data concerning size and characteristics of reservoirs, economic recoverability, technology development, future drilling success, production experience, and other economic and operating conditions. In accordance with the “safe harbor” provisions of the Private Securities Litigation Reform Act of 1995, Marathon has included in its attached Form 10-K for the year ended December 31, 2005, cautionary language identifying other important factors, though not necessarily all such factors, that could cause future outcomes to differ materially from those set forth in the forward-looking statements. 2005: A year of growth across all Corporate Information Corporate Headquarters Section 302 Certifications and NYSE CEO Certification 5555 San Felipe Road Marathon Oil Corporation has filed the certifications of its chief Houston, TX 77056-2723 executive officer and chief financial officer pursuant to Section 302 of the Sarbanes-Oxley Act of 2002 as Exhibits 31.1 and business segments. Marathon Oil Corporation Web site 31.2 to its Annual Report on Form 10-K for the year ended www.marathon.com December 31, 2005. In May 2005, Marathon's chief executive Investor Relations Office officer, as required by Section 303A.12(a) of the NYSE Listed 5555 San Felipe Road (77056-2723) Company Manual, submitted his certification to the NYSE that P.O. Box 3128 (77253-3128) he was not aware of any violation by Marathon of the NYSE's Houston, TX corporate governance listing standards. Kenneth L. Matheny, Vice President, Dividend Reinvestment and Direct Stock Purchase Plan Investor Relations and Public Affairs The Dividend Reinvestment and Direct Stock Purchase Plan pro- [email protected] vides stockholders with a convenient way to purchase additional 713-296-4114 shares of Marathon Oil Corporation Common Stock without Howard J. Thill, Director, payment of any brokerage fees or service charges through Investor Relations investment of cash dividends or through optional cash payments. [email protected] Stockholders of record can request a copy of the Plan Prospectus 713-296-4140 and an authorization form from National City Bank. Beneficial Notice of Annual Meeting holders should contact their brokers. The 2006 Annual Meeting of Stockholders will be held Lost Stock Certificate in Houston, Texas, on April 26, 2006. If a stock certificate is lost, stolen or destroyed, notify National Independent Accountants City Bank in writing so that a stop transfer can be placed on PricewaterhouseCoopers LLP the missing certificate. National City Bank will send you the 1201 Louisiana, Suite 2900 necessary forms and instructions for obtaining a replacement Houston, TX 77002-5678 certificate. You may be required to obtain and pay for the cost of an indemnity bond. If you find the missing certificate, notify Common Stock Exchange Listings National City Bank in writing immediately so that the stop New York Stock Exchange (Principal Exchange) transfer can be removed. To avoid loss, theft or destruction, Chicago Stock Exchange we recommend that you keep your certificates in a safe place, Pacific Stock Exchange such as a safe deposit box at your bank. Common Stock Symbol Taxpayer Identification Number MRO Federal law requires that each stockholder provide a certified Principal Stock Transfer Agent Taxpayer Identification Number (TIN) for his/her stockholder Marathon employees continue to deliver on National City Bank, Loc. 5352 account. For individual stockholders, your TIN is your Social Corporate Trust Operations Security Number. If you do not provide a certified TIN, P.O. Box 92301 Marathon may be required to withhold 28 percent for federal Cleveland, OH 44193-0900 income taxes from your dividends. 888-843-5542 (Toll free) Address Change a successful strategy that sets us apart from 216-257-8508 (Fax) It is important that you notify National City Bank immediately, [email protected] by phone, in writing or by fax, when you change your address. Annual Report on Form 10-K As a convenience, you also may indicate an address change on Additional copies of the Marathon 2005 Annual Report the face of your quarterly dividend check. Seasonal addresses our competitors and creates shareholder value. may be obtained by contacting: can be entered for your account. Public Affairs Exchange of Certificate 5555 San Felipe Road If you have not done so, we recommend you return any USX Room 4150 Corporation or United States Steel Corporation Common Stock Houston, TX 77056-2723 certificates which were issued prior to May 7, 1991, in exchange 713-296-3911 for certificates for Marathon Oil Corporation Common Stock. Dividends Certificates should be sent to National City Bank. Dividends on Common Stock, as declared by the board of Range of Marathon Stock Sale Prices and Dividends Paid directors, are normally paid on the tenth day of March, June, September and December. 2005 Quarter High Low Dividend Dividend Checks Not Received / Electronic Deposit First $48.76 $35.73 $0.28 If you do not receive your dividend check on the appropriate pay- Second 55.58 44.00 0.28 ment date, we suggest you wait about 10 days after the payment date to allow for any delay in mail delivery. After that time, Third 70.83 54.69 0.33 advise National City Bank by phone or in writing for a replace- Fourth 69.21 56.28 0.33 ment check to be issued. You also may contact National City Year $70.83 $35.73 $1.22 Bank to authorize direct electronic deposit of your dividends or interest into your bank account. Upstream Integrated Gas Downstream Exploration: Marathon’s exploration Marathon’s integrated gas business Refining, Marketing and Transportation: activities are focused on adding prof- is adding value through the development Marathon has extensive refining, market- itable production to existing core areas of opportunities created by the growing ing and transportation (RM&T) or down- in the United States, Equatorial Guinea demand for natural gas. The Company stream operations in the United States. and the North Sea, and to developing is linking stranded natural gas resources Marathon ranks as the fifth-largest potential new core areas such as Angola. with areas where a supply gap is emerg- petroleum refiner in the United States and ing due to declining production and the largest in the Midwest. Concentrated Production: Marathon’s production oper- growing demand – particularly in North in the Midwest, Upper Great Plains, Gulf ations, located in eight countries around America. A key component of the Coast and Southeast regions of the United the world, supply crude oil and natural Company’s integrated gas business is States, Marathon’s RM&T operations gas to the growing world energy market. liquefied natural gas (LNG). Over the past are strategically located to serve major Worldwide operations are focused in the three years, Marathon has established markets and include a seven-plant refining United States, Europe, West Africa, Libya an Atlantic Basin LNG business that network with 974,000 bpd of crude oil and Russia. In 2005, worldwide daily pro- encompasses both ends of the LNG throughput capacity, a comprehensive duction averaged 191 mbpd of liquids and process, the liquefaction or source side terminal and transportation system, and 932 mmcfd of natural gas, or 346 mboed. and the regasification or supply side. extensive marketing operations. Key production investments continue in Norway, where the Company is proceeding with the Alvheim/Vilje developments, and in the Gulf of Mexico, where the Company is part of the Neptune development. Contents 02 Letter to Stockholders 08 Integrated Gas 16 Board of Directors 03 Financial Highlights 11 Refining, Marketing & 16 Corporate Officers Transportation 07 Exploration & Production ibc Corporate Information 12 Corporate Social Responsibility 2005 Segment Income as a Percent of Total 2005 Capital Expenditures by Segment 49% 1% 50% 51% 20% 29% Upstream Integrated Gas Downstream Upstream Integrated Gas Downstream 1 Dear Fellow Stockholders: Four years ago, we outlined a strategic plan and a business model to differentiate Marathon from our competitors. We resolved to remain an integrated energy company, to grow new core areas and to establish a profitable integrated gas business. We defined our vision