Is oil useless in the information era?

Oil can be traded for aluminum, or it can be given away for a positive diplo modifier.

Now that you mention it, it does seem strange that nothing at all in the very last stages of the game uses oil. After all, in real life, it's not as though our 21st Century Information Era society has stopped using oil.

So yeah, I guess it comes down mainly to keeping highly-promoted Battleships around, since they don't upgrade into Missile Cruisers. Tanks and Bombers can upgrade, but you might not have enough aluminum to upgrade them all, so oil continues to be relevant.