The average price of diesel has reached its highest level in more than 12 months, new figures show.
A litre of diesel rose to £1.13 at the end of September amid speculation about a cap on oil production, the RAC said.
The average price has not been that high since August 10 last year.
Petrol prices rose around half a pence last month to £1.12 per litre, just short of the highest price of the year.
The price rises mean filling up an average-sized family hatchback with petrol is over £5 more expensive than at the start of the year, while a tank of diesel is £4 more than in January.
The cost of oil – the biggest variable affecting UK fuel prices – went up 8% in September, finishing the month at 48 US dollars a barrel.
Oil producing group Opec reached a deal last week to stabilise the market by slashing output.
RAC fuel spokesman Simon Williams said: “A higher oil price, combined with a weakening pound, is forcing up wholesale fuel prices.
“The wholesale price of diesel is now nearly 9p higher than it was at the start of August, and petrol 7.4p higher. The effect of this to date has been gradually rising pump prices.
“While we don’t envisage an immediate hike in prices in October, a lot depends on how markets react to the recent news of the first production cut by Opec nations since 2008, which marks a major move away from the organisation’s long-term over-supply strategy.
“The announcement has already caused oil prices to jump a little, but until more specific details are available it is difficult to predict what the longer term outlook on pump prices, and therefore impact on motorists, will be.”