Locked gas caps become more popular when gas prices rise, or people worry about vandalism in their communities. The problem with locked gas caps is you should have a key to open them. Just like car keys, house keys and bike lock keys, gas cap keys can easily be misplaced or forgotten. But when you have the key, removing your locked gas cap to fill your tank should be easy. You may need to maneuver the key in a certain way, so make sure to read the manual or try it out before you are on empty. For example, with Stant Locking Fuel Caps, you must make a 1/4-turn of the key to open any of their locks. For older gas caps, you may need to wiggle the key in the hole a little first or make sure the cap is tight before the key can fit in the slot and unlock the cap.
Using a Screwdriver When There's No Key
If you don't have a key, you can use a flat-head screwdriver to remove the locked gas cap. First you will pry off the chrome key hole cover with the screwdriver. Then you can pry the lock mechanism out and remove the gas cap. It shouldn't take too long or too much strength to use a screwdriver to open your locked gas cap. You can also use a screwdriver to remove the lock completely, or you can wedge the tool into the lock's grooves and start turning it to unlock it. When you use a screwdriver, you will probably destroy the locked gas cap, and you will need to purchase a new one. A tire iron, which you may have more readily available if this happens on a road trip, can also be used instead of a flat-head screwdriver.
Other Methods That Have Worked
If you want to keep the lock in one piece without destroying it or prying it open, then you may need to find a locksmith if you don't have the gas cap key. A locksmith can pick the lock just as he would if you locked your keys in your vehicle. Another method you can try, which will destroy the gas cap like the screwdriver method does, is to drill a 1/8-inch hole through the outer part of the gas cap and insert a sharp, pointed drywall screw into the lock. When you feel resistance, you should have locked the two halves together, so you can then screw off the entire gas cap.