However, using methodology that the Securities and Exchange Commission prefers, the company said it added 1.3 billion oil equivalent barrels to proved reserves in the year. That would mean it replaced only 83 percent of its 2004 production and its total reserve levels fell.
Exxon Mobil's production totalled about 1.6 billion oil-equivalent barrels in 2004.
The company has long based its reserves on its own forecasts for the long-term price levels of its resources, said an Exxon spokeswoman. She said Exxon bases its investment decisions on this reserves estimate.
Recently, the SEC has increased its scrutiny of how energy companies report reserves, requiring companies to report reserve levels based on prices at the end of each year.
Don Roesle, president of independent reserves evaluation company Ryder Scott, said most oil companies use a different standard to inform their own business decisions - usually based on average prices or long-term forecasts.
Exxon Mobil, which passed General Electric Co to become the world's most valuable public company by stock market capitalisation on Friday, said the vast majority of its reserve additions in 2004 were from its operations in Qatar. The company also added to its reserves in West Africa, Europe, and the Caspian region.