"According to the Petrol Retailers' Association, there is no difference between the standard petrol and diesel that you buy from either a franchised fuel station or a supermarket forecourt. In many cases, the fuel is sourced from the same refineries and sometimes delivered in the same tankers.
Supermarkets are prepared to sell their fuel at very little or almost no profit in order to tempt shoppers into the supermarket. The theory is that shoppers will think that if it sells cheap fuel, it'll also sell cheap food.
The difference in fuels is in specialist or premium fuels, such as Shell Optimax and BP Ultimate, which contain additives to improve performance and efficiency. When you buy these fuels, you pay for the special ingredients."
There is a lot of nonsense often spoken about Supermarket Fuel by those who think it is inferior, the base stuff is the same as any brand base stuff and as said in the above quote, comes from the same refinery, probably even in the same tanker
