The average price of unleaded petrol has reached a new high of 137.44p per litre, according to industry analysts Experian Catalist.
That just exceeds the average of 137.43p reached in May 2011.
Petrol has been pushed up by oil prices, which have risen in recent months due to tensions over Iran's nuclear plans and unrest in the region.
The weak pound has also been making oil, which is bought in US dollars, more expensive for British buyers.
The price of Brent crude oil hit a 43-month high on Thursday, peaking at $128.40 a barrel in New York.
The average price of diesel, which was already at an all-time high, continued to rise to 144.67p per litre, Experian Catalist said.
Fuel campaigners have called for the chancellor to scrap the 3p a litre rise in fuel duty planned for August.
However, reports suggest that George Osborne is unlikely to alter current plans.
AA President Edmund King said: "This new record for petrol and diesel just confirms what every family and business knows - fuel prices are hurting them badly and there seems no stopping them.
"The AA has asked the chancellor to do what he can to protect the UK economy from fuel market volatility and record high prices which are stemming growth.
"There is no more give in family and business budgets despite them cutting back on fuel purchase and other spending so they can get to work and go about their business."
Meanwhile, a survey by the Countryside Alliance has indicated that the price of diesel in rural areas is, on average, 4p more than in urban areas.
The most expensive diesel was in Purbeck in Dorset and Ryedale in North Yorkshire, where it costs an average 146.9p per litre.
Diesel was cheapest - at an average 139.7p per litre - in North Tyneside, Birmingham and Dartford, south-east London.
The Countryside Alliance said cars were becoming an "unaffordable necessity" for many living in rural communities.