I'm pretty sure petrol means gasoline not petroleum.
replyPetrol is technically just short for petroleum, which is latin for "rock oil"
replyGasoline is from gas + plus the chemical suffix "ol" short for the latin "oleum", and "ine" meaning "made of".
But the etymology of a word doesn't prove that someone is using that word wrong, or people on both sides of the pond would have to start baking our biscuits a second time.
replypetrol !== petroleum
replythe confusion is solely in your reading comprehension skills and not in the GP's use of the words