|It's not only the additives. Oil majors like Shell, BP, Exxon et al do have a tendency to insist on more stringent shipping standards, whereas those that supply supermarkets may cut corners, not so much in terms of ship quality, that is all pretty much of a muchness nowadays, 15/20 years ago, not so much. More in terms of ship cargo history, which although may lead to cheaper transportation costs, can (not necessarily will) lead to product contamination.|
Generally though it's much like anything else. Cheap doesn't always equate with quality. Not so important when you're bunging it in a tractor or a 20 year old car, but the modern ones with sophisticated computer controlled engine management systems tend to be more sensitive.