It’s easier to put petrol in diesel tank than the other way around, but both can potentially damage your engine. This is unfortunate, as petrol can have a worse effect on a diesel engine than diesel has on a petrol. The main issue is that diesel fuel itself is used to lubricate certain essential parts of the car, and that petrol has none of the lubricating qualities necessary to keep components like the fuel pump happy. Petrol and Diesel generally mix together (rather than one fuel floating on top) so once the car starts drawing liquid from the tank, it’s already a problematic cocktail.