Supermarkets have national agreements with the major refiners. These give them wholesale prices, (as you'd expect), plus facilities to pick-up loads of fuel in their own tankers from local depots. So, you might be buying fuel from any of the majors and the supermarket is just a reseller. Tesco undercutting the oil majors by 5p/Ltr is not a great trick. a) they don't have any of the overheads of crude oil exploration/extraction/transport ashore/refining/distribution but they DO have thousands of products to sell you which generate their own, (sometimes excessive), profits. As something like 73% of fuel cost is Government tax + duty, you can work out just how much of that 5p/Ltr is funded by Tesco and how much is funded by you, the taxpayer. Not sounding quite so generous now ?