The RAC said a litre of unleaded petrol sold wholesale for 6p less since the end of August, while diesel was down by 2p a litre, giving petrol stations the power to lower prices.
The car services company explained lower prices were due to a drop in oil prices since Syria agreed to sign a treaty banning chemical weapons and the pound reaching a seven-month high against the dollar.
It comes as official figures showed inflation was down to 2.7%, partly due to a slow down in petrol pump rises.
Petrol prices rose 2p per litre compared with a rise of 3.5p per litre in the same month last year, according to the Consumer Price Index.
But Pete Williams, RAC head of external affairs, said motorists across the UK were watching to see whether retailers would reduce prices by sharing the benefits of lower wholesale costs."