You'll remember some time ago I posted about why cheap supermarket petrol is cheap. Well I have another nugget of information from my delivery driver friend which was news to me, but having been walked through it, it does seem to be true.
If you live in America, you're best buying Chevron or Shell petrol. There's a couple of reasons - both are 'top tier' petrol in terms of additives and detergents. But more interestingly, these are the only two companies who have separate trailer policies for oil and petrol.
So what is a separate trailer policy? It means that Chevron and Shell allocate trailers to carry refined petrol, and trailers to carry unrefined crude, and never mix the two. At the time of writing, they're the only two companies that do this. Every other refiner and distributor does double-duty with their trailers - sometimes they haul crude, sometimes they haul petrol. The key here is that the trailers are supposed to be cleaned thoroughly when going from one cargo to the other but very often they aren't. This means that unrefined crude can end up mixed in with refined petrol, and when that is burned in your engine, it can lead to fouling of fuel lines, filters, pumps and injectors.
So now you know.