Motorists across Oxfordshire yesterday were paying an average of £5 a gallon for petrol for the first time as the price of oil continues to soar.

A litre of unleaded now averages £1.10 on forecourts in the city - nearly 20 per cent more than a year ago when the average price was 92.7p per litre - and motoring organisations could not predict when it would peak.

Diesel has risen to an average of 119.5p per litre.

The price increases mean a driver with a typical 50-litre (11 gallon) tank now has to spend £55 to fill up - £8.65 more than they did a year ago - while the AA said families are spending an extra £38 per month on petrol when compared to 2007.

The increases have forced families such as Gemma Barrett's to ration their use of their car.

Mrs Barrett, a mum-of-three from Lambourn Road in Rose Hill, Oxford, said: "The price of petrol is disgusting.

"It is a real struggle for families to run their cars. We only really use our car for essential journeys now.

"It's ridiculous. The price of petrol keeps going up but our budget can't stretch enough to meet it."

The 24-year-old, whose husband, Jamie, 27, is a delivery driver for Parcelforce in Kidlington, added: "This is penalising people on low incomes. I know two people who've sold their cars now because they can't afford to keep running them.

"My husband only uses our 1.8 litre Vauxhall Vectra to go to work and for food shopping.

"We used to take the kids to see their grandparents in Bicester every week but now we have to ration it to every other week or once a month.

"They say that public transport is better for the environment, but with three children it isn't practical."

Prices at the pump are expected to continue rising after the cost of crude oil nearly reached $120 per barrel on the New York Mercantile Exchange on Monday.

The price rises come as BP announced yesterday its profits had almost doubled for the first quarter of this year from $4.6bn to $7bn and Shell reported a 25 per cent rise in first quarter profits.

Andrew Howard,corr head of road safety at the AA, said the cost of petrol was expected to continue rising while it could take up to three weeks for Monday's crude oil price rise to be felt at the pump.

He said: "We are in new territory now. It appears there's nothing at the moment to stop pump prices going up even higher. We are seeing prices go up daily."

He added: "A lot of journeys that families make are not easily avoidable and they are being forced to make savings elsewhere in order to keep buying petrol."