In my local Asda (Ellesmere port) they have a sale (nation wide I assume) on Mobil Oil.
They have 5lt Mobile Super M 15w-40 reduced from £22 down to £10
5lt Mobile Super S 10w-40 Semi-synthetic reduced from £22 down to £10 too.
Cheaper than Asda's own brand which I think was £14 for the same size, good price for a good named oil. There were other Mobil types but only them two were reduced.