At first, the project will be tested at six sites to be redeveloped in southern England. Shoppers will be able to buy a range of fresh foods, oven-ready meals and lubricant top-up lines.
Ian Sutcliffe, Shell UK retail manager, said: "This trial gives us the opportunity to combine the strengths of our respective brands."
Mark Rollman, senior manager of Sainsbury's, said: "We've worked hard to develop a range of store formats to fit our customers' needs."
The decision underlines Sainsbury's efforts to move into the automotive sector. It has launched a nationwide car purchase scheme that finances cars from franchised dealers through Sainsbury's Bank.
It also underlines steady growth in the variety of products sold on forecourts. According to the 2000 Retail Marketing Survey from Portland Press, there are 13,716 filling stations in the UK, of which 1,013 are operated by supermarket chains.
A total of 10,608 forecourts already incorporate shop premises of more than 10 sq. m. and 718 have fast-food outlets such as Little Chef or McDonald's attached.