Asda has admitted drivers paid just 12.9p a litre for petrol after staff put a decimal point in the wrong place.
The blunder at the Rooley Lane site in Bradford, West Yorkshire happened on a self-serve pump after the 24-hour site switched over to just pay@pump for the night shift.
About 50 motorists were able to fill up with unleaded fuel on Thursday night for two hours until the mistake was spotted by staff in the main store.
Asda then closed the site until 7.30am to ensure the problem was properly fixed.
A spokeswomen for Asda said: “It cost us some money but we are quite pleased that some customers were able to take advantage of it. Our customers are pretty savvy shoppers anyway.”