Q4 2005 they paid in excess of $7 billion in taxes
Note however that Exxon is a multinational, and pays taxes all over the place, with various credits for various taxes. So whatever number you see at the bottom won't be what they pay to the IRS. In some countries, they may get credits (if they lost money in one particular country, they may get a NOL carryforward depending on the tax laws of that jurisdiction).
The notes to the financial statement may breakdown where taxes were paid.