Morrisons is cutting its price by 10p a litre to 99.9p for customers who spend at least £50 on their supermarket shopping.
Diesel drivers will pay just over £1 per litre as part of the promotion.
This will be the first time petrol has dropped below the pound mark since the Brexit vote.
Services director for Morrisons, Roger Fogg, said: “With Christmas around the corner, our customers tell us they very much welcome our help in reducing the cost of their fuel. That’s why we are turning the clock back to the start of this year when petrol prices were typically below £1 a litre.”