Sainsbury's said it was cutting petrol by 5p a litre from Thursday for customers who spent £50 or more in stores. The promotion will run for two weeks.
The price of a barrel of oil dropped from a peak of 147 dollars to 130 dollars in recent weeks.
Asda said all 170 of its petrol forecourts across the country would sell unleaded petrol for 113.9p a litre and diesel for 128.9p a litre from today.
Asda trading director David Miles said: "We are seeing a more stable reduction in oil prices, allowing us to pass on the savings to customers."
Morrisons' move came into effect at 6pm yesterday.
AA president Edmund King said: "Since mid-July, the wholesale gasoline price has fallen six per cent and the AA expects fuel suppliers to pass on, not pocket, the saving for the good of UK families."