Most Warrnambool service stations were charging between 190 and 192 cents per litre for unleaded petrol on Friday, sharply cheaper than in Melbourne.
However, the price has dropped to under 180 cents per litre at some Portland outlets.
RACV head of media and communications Eleanor Colonico said the majority of petrol retailers in Warrnambool are selling unleaded fuel for 191.9 cents per litre or less.
"This is cheaper than the average price in Melbourne, which sits at 202.8 cents per litre," Ms Colonico said.
"Adelaide's average for unleaded fuel sits at 170.2, Brisbane's average is 185.6, Canberra's average is 217.1, Darwin's average is 208.3, Hobart's average is 202.8, Perth's average is 182 and Sydney's average is 187.5."
Ms Colonico encouraged motorists to shop around to get the best deal.
"The trend for fuel prices is difficult to predict and will depend on a range of factors including geographical area, availability, international benchmark prices, taxes, the value of the Australian dollar relative to the US dollar, and levels of competition in different areas," she said.
The federal government cut the fuel excise in half back in March, but this discount is expected to expire at the end of September.
The excise cut resulted in a saving of about 22 cents per litre.
Midfield Group spokesman Dean McKenna said the rising cost of fuel was a concern for his business - like many others.
"The rising cost of fuel has added about 40 per cent to our freight costs," Mr McKenna said.
He said that increased amount to "many millions of dollars".
Treasurer Jim Chalmers said this week the cut to the petrol excise, which due to end in September, could not be continued forever due to the state of the budget.
"There are serious pressures on the budget; it would cost some billions to extend it even for another six months. And so we need to be up front about that and we need to be responsible about it," he told the ABC.
"What we're seeing now is the wholesale international price of petrol has come off a bit.
"We call on the service stations to pass those savings on because Australians should be getting that petrol price relief now and not just reliant on the program that runs out in September."
The treasurer's concerns come with the Australian Energy Market Operator (AEMO) triggering the gas supply guarantee on Tuesday evening to secure supply from Queensland after shortages in Victoria.
Reserves at Victoria's Iona gas storage facility in Port Campbell have dropped to record low supply levels due to high demand amid the state's price cap.
Lochard Energy, which owns Iona, says "unplanned coal fired generation outages" and cold weather has increased demand.
"It is the case that gas supply and winter peaking capacity are becoming increasingly tighter on the east coast," Lochard said in a statement.
The opposition's treasury spokesman Angus Taylor says more gas is needed in the system immediately instead of the demonisation of fossil fuel companies.
"Yes, new technologies are emerging, yes we're investing in them, yes Australia's leading the world on many of those, but gas is part of the answer in the short to medium term," he told Sky News.
"If you want to get more renewables into the system, you've got to have a flexible dispatchable fuel source in large quantities and gas provides that so everyone needs to get on board, work with the gas producers, don't demonise them."
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