Oil storage tanks and refining facilities sit at a refinery operated by Exxon Mobil Corp.

Exxon Mobil on Friday said it could write down billions of barrels of reserves, marking a change of course as the company faces federal investigations into how it values those reserves.

During the third quarter, The Wall Street Journal reported that the Securities and Exchange Commission and New York Attorney General Eric Schneiderman's office launched probes to determine if Exxon should have written down the value of its reserves based on drop in global oil prices that began about two years ago. Unlike peers such as BP and Chevron, Exxon has resisted reducing its assessment of how much its reserves may be worth.