The gap between prices in country districts compared with urban areas has closed from around 5p a litre to as low as 2p, according to the AA.
This dip in rural prices has contributed to a general nationwide fall in the cost of petrol, which now averages 129.63p a litre compared with 130.46p in mid-January.
The lowest petrol price over the past four weeks was 129.30p a litre on February 2 - the lowest average figure since February 2011.
Diesel now costs an average of 137.02p a litre, compared with 138.24p in mid-January.
The AA said the strengthening of the pound against the dollar had accounted for much of the drop in pump prices. Yorkshire and Humberside has the cheapest petrol - at an average of 129.2p a litre, but Scotland has the most expensive diesel at 137.6p.
AA president Edmund King said: "Across whole towns, for months if not years, drivers and businesses have been charged 4p to 6p a litre more for petrol compared to what retailers charged for the same fuel in neighbouring towns. Drivers don't know whether to rejoice or get very angry that supermarkets and other fuel markets can actually trade at 2p to 3p a litre above prices in cheaper areas."