Checking it twice

You know when you are driving someone else's car are you are not sure whether it is petrol or diesel. I think the petrol nozzle can fit into a diesel fuel filler neck but the diesel nozzle cannot fit into the petrol fuel filler neck. I was with someone one time who had put the wrong fuel into a minibus. Luckily it was picked up when he went to pay for the fuel and he had not started the vehicle. Still it was a costly mistake getting the tank drained.