Petrol prices have climbed to their highest level in two years, according to the RAC.
Retailers may be charging more to make up for lower fuel sales during the pandemic, it said.
Pump prices fell in May 2020 to a low of 106p as oil prices plummeted, but motorists had to abide by travel restrictions.
The average cost of a litre has since soared to 129.27p, the highest level since August 2019.
The cost of a litre of unleaded is now more than 22p more expensive than a year ago - the biggest 12-month increase seen for 11 years.
"After seven consecutive months of rising prices drivers will be wondering if the increases are ever going to end," said RAC fuel spokesman Simon Williams.
He said motorists have faced the biggest petrol price rise in any 12-month period since May 2010 when unleaded rocketed from 99p a year earlier to 121p.
Unleaded petrol has climbed 2p in the last month and 15p since November, since when prices have climbed every month.
That has left motorists paying £8 more for a full tank of petrol than seven months ago.
Diesel prices are climbing slightly less rapidly, up just less than 20p a litre over the last 12 months.
Will prices continue rising?
"Looking at the wholesale price of both fuels, in normal circumstances unleaded definitely shouldn't be continuing to rise with the numbers actually pointing to the potential for a 2p reduction," said Mr Williams.
He added that diesel is currently 4p too expensive "which suggests retailers are using the saving in the wholesale price to help make up for lower fuel sales over the last year".
The future of fuel prices is hard to predict more than a few weeks in advance and even more so now as the pandemic appears to have altered the dynamics of fuel retailing, he said.
Supermarkets have an even greater share of the market, according to the RAC.
Buying fuel at a forecourt run by one of the four major supermarket chains will currently save drivers around 4p a litre with the average price of petrol standing at 124.83p and diesel 127.36p.
"We urge retailers not to take advantage of drivers and fairly reflect what's happening with wholesale prices on the country's forecourts," he said.
Luke Bosdet, the AA's fuel price spokesman, said: "Oil prices rising back above 70 US dollars a barrel casts a shadow over staycation travel, with petrol prices at their highest for 20 months.
"The speed of the price rises at a time when drivers are beginning to travel much longer distances is a post-lockdown shock for many."