British supermarkets have slashed the price of diesel for the second time in a week.
Last week's price drop meant that for the first time in 15 years, the fuel was cheaper than petrol.
But today Morrisons and Tesco said that they would be reducing the cost of diesel by a further 2p, with Sainsbury's set to make the same reduction across its 300 forecourts tomorrow.
This is the third time in less than three weeks that both Sainsbury's and Morrisons have dropped the price of the fuel.
The move was welcomed by Steve Gooding, director of the RAC Foundation.
He said: "This is welcome news but has been a long time coming. The wholesale price of diesel dropped below that of petrol back in May but only in the past week or so have we seen this starting to be reflected at the pumps.
"We would hope this is not the end of the reductions as the price of diesel at the refinery gate is still 4p per litre cheaper than that of petrol."
Avishai Moor, Sainsbury's head of fuel, said: "From tomorrow we're once again dropping the price of diesel by up to two pence per litre at all our petrol stations. We know that fuel is a big expense, especially during the summer holidays, and we are committed to helping our customers go further for less."
Morrisons said that its latest round of cuts meant that diesel prices are now 21 pence a litre cheaper than 12 months ago.
Mark Todd, petrol director for Morrisons, said: "Further wholesale price drops mean that we can pass more savings on to our customers. We will continue to look for opportunities to pass on savings on unleaded as soon as we can."
Tesco's prices will come into effect across 500 filling stations at 1pm today.
However, Asda said that it had no immediate plans to drop its prices, after announcing last week that drivers would pay no more than 112.7 pence per litre across its 272 filling stations.
Mr Gooding continued: "The price of fuel is a headline cost for motorists and one they keep an eagle eye on.
"With that in mind we expect other retailers to also move their pump prices downward. Frankly it would be a surprise if they didn't."