Every vehicle in Codename Eagle runs on Fuel.
When low on fuel, a red icon with a fuel tank will appear. This means that while you can still operate normally, you will soon run out of fuel.
A vehicle out of fuel will not be able to move until it is refueled.
Planes out of fuel will have their engine cut out - however, it is still possible to fly, as you ride on the wind, but you will slowly float downwards.
Picking up a fuel item will place it in your inventory. Use a fuel tank next to a vehicle without full fuel, and you will fill up part of the vehicles fuel tank. Fuel pickups are one use only.
Fuel tanks are usually next to every plane in every multiplayer map. They are commonly found in bases and in plane hangars.