Have you ever pulled into a gas station only to discover that your fuel door is on the opposite side from the pump? It may seem like carmakers chose randomly, but there is actually no universal rule requiring fuel fillers to be placed on one particular side. Automakers choose the location based on the vehicle’s overall design, engineering, safety, and manufacturing requirements.

Underneath a car is a tightly packed network of components, including the fuel tank, exhaust system, suspension, brakes, wiring, and structural parts. Engineers must determine how everything can fit safely and efficiently. The fuel-filler neck also needs a practical route between the fuel door and the tank, so placing it on one side may make more sense for a particular vehicle.

The exhaust system can also influence the decision because engineers need to manage heat and keep fuel-system components appropriately protected. Crash safety, emissions requirements, and fuel containment are additional considerations. Once a vehicle’s structure and fuel system have been designed, changing the location of the fuel door can require significant modifications.

That’s why even vehicles from the same manufacturer can have fuel doors on different sides. Different models may use different platforms, layouts, and engineering solutions. The driver’s side isn’t automatically preferred, and some vehicles place the fuel door on the passenger side simply because that arrangement works better with the rest of the design.

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 triangle or arrow beside the symbol indicating the side where the fuel filler is located. So the next time you’re at a gas station, that tiny dashboard indicator can save you from pulling up to the wrong side of the pump.