Have you ever pulled into a gas station only to realize that your car’s fuel door is on the opposite side from the pump? It may seem random, but there is no universal rule requiring automakers to place fuel fillers on one particular side. Engineers choose the location based on the vehicle’s overall design, safety requirements, and manufacturing considerations.

A car’s underbody contains many important components, including the fuel tank, exhaust system, suspension, wiring, brakes, and structural parts. Engineers also need to route the fuel-filler neck safely between the fuel door and tank, while considering exhaust heat and crash protection. In some vehicles, placing the filler on one side simply works better with the way everything else is arranged.

Manufacturing can also influence the decision. Moving the fuel door may require changes to the body, fuel lines, or production process, so manufacturers generally choose the location that fits the vehicle’s existing design. That is why even models from the same company can have fuel doors on different sides, and the driver’s side is not automatically the standard choice.

Fortunately, you don’t have to remember where your fuel door is. Just look at the fuel-pump symbol on your dashboard: a small triangle or arrow beside it indicates which side the fuel filler is on. That tiny indicator can save you from pulling up to the wrong side of the pump and makes a small but useful part of driving a little easier.