Last week's federal budget halved fuel excise to 22 cents a litre as part of an $8.6 billion cost-of-living package.

Australian Competition and Consumer Commission chair Gina Cass-Gottlieb said the fuel excise cut is being passed on in full by wholesalers through reduced prices to retailers.

"Over the next weeks, as petrol stations use up their stocks of fuel on which the higher excise had already been paid, we expect the reduced wholesale price to be passed through at the bowser everywhere," she said.

However, an ACCC analysis found significant falls in retail prices have already occurred in the major capital cities.

It found between March 29 (budget night) and April 5, average daily regular unleaded petrol prices fell by between 25 and 27 cents per litre in Sydney, Melbourne and Brisbane, by around 31 cents in Adelaide, and by 35 cents in Perth.

Retail prices are influenced by a number of factors including the level of excise tax, as well as reflecting movements in international refined petrol prices, and the foreign exchange rate.

"Despite the various factors impacting the fuel price, our analysis indicates that clearly a major part of the reduction in excise has already been passed through in the major capital cities," Ms Cass-Gottlieb said.

Prices have also fallen in the smaller capitals of Canberra, Hobart and Darwin, dropping by between 19 and 24 cents per litre, while prices in many regional centres are also lower.

"It will take some time for petrol stations with lower turnover to use up existing stocks of petrol and diesel, and restock with fuel at the reduced wholesale price that takes account of the excise cut," Ms Cass-Gottlieb said.

Australian Associated Press