Costco gas

here in england,our supermarkets sell petrol at a few pence per litre less than the “big brands”,such as shell,b.p,etc…but it is base fuel with no additives,so personally i always use a named brand of petrol because they contain detergents that help to keep your engine,and fuel injectors clean,so that your engine performs at its best.the cheap fuel wont necessarily do any damage,but over time there will be carbon build up,reducing engine power and economy,so its worth spending a little more for the sake of a smooth running,efficient engine.