Motorists will now pay less for fuel at many supermarket forecourts as Tesco, Asda, Sainsbury's and Morrisons have all cut their petrol and diesel costs.
Last week Morrisons was the first to cut prices, with unleaded down 2p a litre, and diesel down 1p.
Tesco's cut of up to 2p per litre came into effect at its 500 forecourts last night, while Sainsbury's has put its own prices down by up to 2p at its 303 stations today.
Asda introduced a national price cap yesterday, meaning motorists won't shell out more than £105.7/L on unleaded and £106.7/L on diesel at any of its 272 stations. The cap will mean prices fall by up to 2p a litre in some areas.
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Is Brexit affecting fuel prices?
The wholesale cost of oil has slumped in recent weeks, but forecourt prices across the UK have remained largely the same until now, according to the RAC.
Motoring campaign group FairFuelUK claims fuel suppliers are using Brexit uncertainty as an excuse to avoid passing on their own savings to consumers.
FairFuelUK co-founder Quentin Wilson says: "Petrol margins at the pumps have doubled since Brexit. The whole fuel supply chain cartel seems to be colluding behind a smokescreen of post-Brexit uncertainty."
Last month, the RAC claimed there was a "compelling case" for price cuts on forecourts and said it hoped retailers were not taking advantage of public perceptions that fuel prices would rise after Brexit.
Morrisons services director Roger Fogg says the retailer is doing all it can to hold down prices amid "post-Brexit fuel price uncertainty".
"When we can make savings we will pass it on to customers," Fogg adds.
Andy Peake, Asda's senior director for petrol, says: "It's great to see that costs have dropped despite early predictions that the cost of fuel would increase following the outcome of the EU referendum".
Tesco, Sainsbury's and Asda say their price cuts are aimed at helping customers enjoy their summer holidays.
Additional reporting by the Press Association.