It’s far harder to put Diesel in a Petrol Car than it is to put petrol in a diesel car. That’s because the nozzle of a diesel pump won’t generally fit into a petrol tank, which gives petrol car drivers some protection against this type of misfuelling. Obviously if refilling your car from a jerry can, or if either the pump or the tank don’t comply with convention, you can still make the same mistake, but the vast majority of misfuelling events are petrol into a diesel tank.