Average diesel prices have risen above £1 a litre to a record high as the cost of crude oil continues to forge higher.
Prices differ across the country
A litre of diesel, which fuels around a third of UK vehicles, now costs an average of 100.15p, according to the AA and industry researchers Catalyst.
With oil prices now above $90 a barrel, experts says it is only a matter of time before petrol prices follow suit.
The average price of a litre of unleaded petrol is now 97.92p, just below its record high of 98.54p.
The price of oil is rising amid tension over possible military action by the Turkish army against Kurdish rebels in Iraq and as a weak dollar makes oil a cheaper investment.
The previous peak for diesel was in August 2006.
Petrol retailers have warned of escalating prices as wholesale crude prices soar and the impact of rising fuel duty makes itself felt.
Duty rose by 2p a litre at the start of the month, adding pressure to consumers and businesses already facing high fuel and energy bills.
The cost of petrol continues to differ significantly across the UK, with Londoners paying an average of 98.2p a litre, 1.7p more than in drivers in Scotland.
The AA said people were paying 11.13p per litre more for petrol than a year ago.
"Looking at what's happening in the oil market, it's reasonable to assume that petrol prices will also at some point break that £1 barrier," said the AA's head of public affairs, Paul Watters.