The price of petrol at the pump rocketed by a "hellish" 6p a litre in May - the worst monthly rise for 18 years, the RAC has said.
Unleaded shot up from 123.43p to 129.41p a litre, putting the cost of filling up a 55-litre family car to £71.18.
The increase equalled £3.29 in just one month, data from RAC Fuel Watch shows.
The average price diesel per litre saw a slightly greater monthly increase of 6.12p, from 126.27p to 132.39p, which was the second-worst rise since the start of 2000.
The cost of a tank of diesel for a family car became £3.37 more expensive during May, at £72.81.
The average prices of both petrol and diesel have gone up every day since 22 April, the motoring group said.
RAC fuel spokesman Simon Williams said: "May was a hellish month for motorists.
"Sadly, they have been besieged by pump price rises for three months, with nearly 9p a litre being added to petrol since the beginning of March.
"The rising oil price together with a weaker pound is a punitive combination for anyone that drives regularly.
"For many people there is little alternative to the car for the majority of journeys they have to make, so it is therefore very difficult to avoid feeling the pinch of rising pump prices."
The so-called big four supermarkets - Tesco, Asda, Sainsbury's and Morrisons - raised petrol by 5.49p a litre and diesel by 5.88p in May.
Motorway service stations added 6.37p to unleaded, making it 144.75p a litre, and 6.69p to diesel making a litre 147.80p.
The price of oil passed the 80 dollar a barrel mark (£60) two times during the month.