Locked gas caps come in various sizes to fit a variety of automobile makes and models. A typical cap costs anywhere from £9 to £16. Having a locked gas cap can prevent gasoline thieves from siphoning your fuel in the middle of the night, but locked gas caps can sometimes be tricky to open even for the cars' owners.
Use the key. Turn the key clockwise, then back to the left. Remove the key and spin the cap off so you can begin to refuel your vehicle.
Freeze the cap. If the cap is stuck or locked on a filler neck and you do not have the cap key, pour cold water over the cap. Let the water freeze by placing ice over the cap or waiting one to two hours during winter for the cap to freeze on its own. After the water has frozen, spin the cap off the same as you would if it was unlocked.
Use a pair of pliers. Tighten your grip on the cap to keep it from spinning. Use a pair of pliers to turn the cap counterclockwise. Continue to turn the cap to the left until it spins off.
Call a locksmith. If you have misplaced the cap key and are unable to open the cap, call your local locksmith. The cost of using a locksmith might run you from £48 to £65 depending on the part of the country you live in and what locksmiths charge in your area.