Ever wondered why your car’s fuel door is sometimes on the opposite side from the gas pump? It isn’t random. There is no industry-wide rule requiring fuel fillers to be placed on a specific side, so automakers choose the location based on the vehicle’s design, engineering, safety, and manufacturing requirements.

Underneath a car, engineers must fit many components into limited space, including the fuel tank, exhaust, suspension, wiring, brakes, and structural parts. The fuel-filler neck also needs a practical route from the fuel door to the tank. Exhaust placement, heat management, crash protection, emissions requirements, and the existing body design can all influence which side works best.

That’s why even vehicles from the same manufacturer can have fuel doors on different sides. Fortunately, you don’t have to remember which side yours is on: simply check the fuel-pump symbol on the dashboard. A small triangle or arrow beside the symbol indicates the location of the fuel filler—an easy detail that can save you from pulling up to the wrong side of the pump.