Have you ever pulled into a gas station, reached for the pump, and realized the fuel door is on the opposite side? It can seem completely random—some cars have it on the left, others on the right. But there’s actually a good reason: there is no universal rule requiring automakers to put the fuel filler on one particular side.

When engineers design a vehicle, they have to fit the fuel tank, exhaust, suspension, wiring, brakes, structural components, and fuel lines into a limited amount of space. The shape and position of the fuel tank can make one side more practical than the other. Engineers also have to consider crash protection, emissions requirements, heat from the exhaust system, and how easily the vehicle can be assembled.

That’s why even vehicles from the same manufacturer can have fuel doors on different sides. The decision is usually based on the overall architecture of that particular model rather than simply choosing the driver’s side. In some situations, having the filler on the passenger side can also keep the fuel door farther from traffic if a driver ever has to refuel near a roadway.

Fortunately, you don’t have to remember which side your fuel door is on. Look at the fuel-pump symbol on your dashboard. Many vehicles have a small arrow or triangle beside the icon pointing toward the side where the fuel door is located. So the next time you pull into a gas station, check that little arrow first—it could save you from having to awkwardly stretch the fuel hose across your car.