If you're planning on filling up your car with petrol, wait until tonight at Tesco or until tomorrow at Asda or Morrisons as the supermarkets are cutting fuel prices by up to 2p/litre.

Asda has sparked a petrol price war by announcing it will cut unleaded and diesel prices by up to 2p/litre from tomorrow. As it sets a national price cap across its 240 forecourts, drivers will pay no more than 124.7p/litre for diesel and no more than 120.7p/litre for unleaded.

Tesco quickly followed suit by announcing it too will cut diesel and unleaded prices by up to 2p/litre cut from 7pm tonight, sooner than Asda.

Morrisons was next to say it would cut the cost of both unleaded and diesel by up to 2p/litre at its 332 petrol stations. Unlike Asda however, Tesco and Morrisons do not set a national price cap so pump prices vary regionally.

Asda says the price cut means petrol prices at its forecourts are at their lowest price since December 2010, and adds that since September this year it has slashed prices by 6p/litre.

It says its petrol price cuts are due to the continuing fall in oil costs–- the price of a barrel of Brent crude oil dropped to under US$85 today.

MoneySavingExpert.com has asked Sainsbury's if it also plans to cut prices and we will update this news story as soon as we hear anything.

However, tomorrow's price drop doesn't necessarily mean that Asda and Tesco are the cheapest fuel providers for you. To find the lowest price in your area, use the website Petrolprices.com and see our Cheap Petrol and Diesel guide for more ways to save when filling up your tank.

According to the latest figures from Petrolprices.com, the average UK price for a litre of diesel was 129.11p/litre yesterday, while the cost of unleaded petrol stood at 124.89p/litre.