Data collected by the Australian Competition and Consumer Commission shows motorists could have saved up to $350 each - or $275 million collectively - last year if they had shirked the big brands and chosen independent retailers instead.

"Independent chains were the lowest priced retailers in all eight [capital] cities, while Coles Express was the highest priced retailer in almost all cities," ACCC Chair Rod Sims said on Thursday.

The ACCC report pits retailers head to head in three separate categories, supermarket chains (Woolies and Coles), refiner-marketers (BP and Caltex) and major independents (7-Eleven and United).

Between the supermarket chains, Woolworths was on average 3.5 cents per litre cheaper than Coles Express, blowing out to a six per cent difference in Sydney.

Caltex was consistently cheaper than BP, but only by 0.9 cents on an Australia-wide average.

In the battle between the two biggest independent retailers, United came out on top averaging 3.3 cents cheaper across all eight major cities.

But not everyone fills up based on price. Convenience and other related offers like loyalty programs and discounts also played a role in where motorists get their fuel.

The best way to find cheap petrol in your area is to download fuel price comparison apps and to regularly check them for the best deals, according to the ACCC.

"Consumers do not only benefit from the lower prices they find using these apps, but they also help reward retailers who actively compete on price," Mr Sims said.

Australian Associated Press