Fuel is the material or substance that when combusted is used to power vehicle engines, typically petrol or diesel in the case of automobiles, or aviation fuel for helicopters and aircraft. In the majority of games throughout the Battlefield series vehicles do not have an associated fuel mechanic and are able to stay powered indefinitely.
Fuel was introduced as a mechanic in Battlefield V specifically for the Firestorm gamemode. In Firestorm, all ground and air vehicles have a limited amount of fuel that depletes when the vehicle is occupied. When all fuel is expended the vehicle may no longer move.
Fuel Canisters can found in the game world and can be used to replenish the fuel bar of vehicles allowing them to be used longer. Once obtained, players can equip and resupply vehicles. During a resupply, the contents of the canister will slowly drain to zero.