Retail fuel sales for the period January to June dipped 5.8%, or nearly 512 million litres, compared with the same period last year, Government figures highlighted by the AA showed.
However, diesel sales for the first half of this year rose 6.6%, or by nearly 270 million litres.
The AA said petrol sales in the first six months of 2013 were more than 25% lower than in the first half of 2008, just before the credit crunch.
Diesel sales in the first half of this year were 3.6% higher than in the January-to-June 2008 period.
AA president Edmund King said: "It would be too easy to blame the collapse of UK retail petrol sales on car-owners switching from petrol to diesel engines.
"These new Government fuel retail sales figures, when set against changes in the number of petrol and diesel cars on the road, show that soaring fuel prices have had by far the greater impact on pump sales since 2008.
"That is why it is critical for pump prices to drop as quickly as wholesale costs allow. The financial well-being and survival of drivers, consumers, business, Government duty revenue and, yes, fuel retailers depend on it."
The figures were released after major supermarkets cut the price of petrol.
Sainsbury's reduced the cost of diesel by up to 4p a litre and petrol by up to 6p a litre, meaning motorists using a Sainsbury's forecourt will pay no more than 129.9p a litre for petrol and 136.9p for diesel.
Asda has also announced a price ceiling at 128.7p a litre for petrol and 135.7p for diesel. Tesco then followed suit, stating it was cutting its petrol by up to 3p a litre and its diesel by up to 2p.