The Sainsbury's chief executive claims fuel prices are close to falling below £1 a litre.
Mike Coupe, chief executive of the supermarket chain, made the prediction as Brent crude was being traded at below 50 US dollars a barrel for the first time since 2009.
The news comes as Chancellor George Osborne declared motorists should be getting the benefits of seven-year-low oil prices passed on to them at the pumps.
Mr Osborne, discussing cheap crude oil at Monday's cabinet meeting, promised an inquiry into its effect on forecourt petrol prices, air fares and heating bills.
Ministers said that they are watching retailers "like hawks".
They said that measures are being considered against energy firms which do not pass price cuts on to their customers. But energy sector officials claim this is already happening.
Mr Osborne said he welcomed the latest move from the four leading supermarket to slash petrol prices by 2p a litre, saying it is "vital" that the savings are passed on.
But many motoring organisations say that more action is needed to help the hard-pressed motorist.
RAC fuel spokesman Simon Williams said: "The price of a barrel of oil looks set to continue to fall as more oil is produced than the world needs. Unfortunately the pound is losing value against the dollar which is undermining some of the benefit of the lower oil price.
"If the pound remains strong and the oil price keeps moving down we are hopeful it will not be too long before one of the leading fuel retailers decides to be the first to offer petrol for £1 a litre - a pump price last seen in late May 2009."
Copyright Press Association 2015