Petrol prices may rise by as much as 18.7 pence per litre following a Brexit vote in the upcoming referendum, according to AA analysis released exclusively to the Press Association.
The study stated that this "worst case scenario" could become a reality if a fall in the value of sterling as a result of the UK pulling out of the EU is combined with a rebound in the price of oil.
A Goldman Sachs report published earlier this month predicted that the pound could tumble by up to 20% in the wake of Brexit.
The AA warned that could mean a two-car family who refuel twice a month would pay £494 more for petrol each year if it happened alongside a rebound in the price of oil to more than 90 US dollars.
It said this could occur if oil cartel Opec agrees production limits and US drivers continue to increase petrol consumption.
The fall in the value of the pound could lead to a £137 rise in the cost of filling up even without any change in oil prices, the AA found.
The referendum is expected to be held on June 23.
Edmund King, AA president, said: "We don't take a view as to whether the UK should leave the European Union as that is up to the people to decide in a referendum.
"However, even before the referendum vote, it seems that financial reports suggest leaving the EU could lead to a sharp fall in the value of the pound which in turn could hit pump prices within days.
"The instability of the pound - combined with Opec countries already looking to freeze oil output and the usual increase in fuel use during the US motoring season - could mean a significant hike in petrol costs."