There's a "very good chance" petrol prices could fall to £1 per litre, or even below, the RAC has said.
The average petrol price is currently £1.07 per litre, but some supermarkets are already selling petrol at £1.03 per litre.
A recent 2p drop in wholesale fuel prices could be passed on to consumers within a few weeks, the RAC said.
According to RAC figures, the last time petrol fell below £1 was in the summer of 2009.
A sharp fall in crude oil prices since last summer is behind falling prices at the pump. Brent Crude is now trading at around $44 per barrel.
"We've seen the wholesale price of petrol and diesel drop by a couple of pence recently," RAC chief engineer David Bizley told the BBC.
"There's typically about two weeks lag in the system. So there's a very good chance that within a few weeks people will be selling fuel at £1.01, and then the temptation to move that extra penny or so will be unavoidable," he said.
Supermarkets use competitive petrol prices to bring people into their stores, he added.
Since June 2014, oil prices have more than halved, falling from more than $100 per barrel.
In the UK petrol prices are also affected by how the pound is trading against the dollar, and taxation. UK fuel duty has been frozen since 2011.