The average price of diesel is expected to fall by 5p per litre (ppl) in the next fortnight, while petrol should fall to £1 for Christmas, suggests the RAC.
Diesel is already at a six-year low, with the average price reaching 109.18p on Friday.
The motoring organisation is urging retailers to ‘do the right thing’ and pass on savings in the wholesale price brought about by oil falling below $40 a barrel for the first time since February, 2009.
Britain’s supermarkets and cheapest fuel retailers are expected to start passing on the savings during the next week.
RAC Fuel Watch data shows oil slipped even further following OPEC’s meeting in Vienna on Friday, where delegates dismissed cutting production to stabilise the price.
The end of day price for a barrel of Brent crude fell from $41.80 last Friday to $39.77 on Monday. Twelve months ago a barrel cost $65 and in June, 2014, it was $115.
This led to significant reductions in the wholesale price of both unleaded and diesel, which the RAC believes will lead to a cut of 3p a litre in the average price of petrol and 5p a litre off diesel, taking average prices to around 103p for petrol and 104p for diesel.
At these prices motorists would be saving around £9 on tank of petrol for an average 55-litre family car compared to this time last year, and more than £11 for a tank of diesel.
RAC Fuel Watch spokesman Simon Williams said: “With the price of wholesale unleaded dropping due to oil falling below $40 the climate is right for £1 a litre petrol, all we need is for the supermarkets to do the right thing and embrace the season of goodwill by passing on those savings at the pump to make Christmas that bit cheaper for everyone.
“Motorists have already enjoyed petrol at under £1 as one supermarket cut prices at its 277 nationwide forecourts as part of a three-day promotion at the end of November, but this should now become a common sight across the country.
“If retailers don’t pass on the savings quickly, they will be giving themselves an unpopular Christmas boost to profits by pocketing the extra margin when they should really be passing this on to their customers instead.
“The long-term outlook is for the oil price to stay low. OPEC is not due to meet again until June 2016 so unless an extraordinary meeting is called, it is anticipated production will continue to outpace demand and in turn keep wholesale fuel prices low.”