Currently in conflict, fuel is barely an issue for several reasons.

The island is quite small, so even with the accelerated fuel burn built into conflict, you rarely run out of fuel.
Infinite fuel can be had at any base just by building a very cheap fuel depot (currently just 150 supplies)

Gameplay could be enhanced by simply making fuel supplies only available from the main base, and a few fuel depots on the island. Players would then need to use fuel trucks to supply fuel to bases and front lines. Refueling points could still be built at bases, but these would arrive empty and need to be supplied by fuel tankers.

This could add another strategic element to the game, similar to how in real life fuel is a critical resource for modern armies.