The competition watchdog's second GROCERYchoice survey has found Coles is still the cheapest supermarket in most regions across Australia.
The September survey found Coles was the cheapest in 40 of the 61 regions surveyed.
But the supermarket giant's margin has dropped slightly compared to August, when 52 of the 61 regions showed Coles as the cheapest.
The price difference between Coles, Woolworths and the independent supermarkets has narrowed as well, according to the Australian Competition and Consumer Commission.
"GROCERYchoice helps consumers find out something supermarkets won't tell them, who is the cheapest overall," Assistant Treasurer Chris Bowen told AAP.
The latest figures showing Coles was still cheaper in two thirds of all regions showed that GROCERYchoice was "helping consumers to make well-informed decisions", he said.
"This is vital information that consumers can throw in the mix - alongside the quality of goods and customer service - before they decide where to shop," Mr Bowen said.
"Another benefit of GROCERYchoice has been to increase competitive tension in the grocery sector, driving the consumer dollar further."
The latest survey found ALDI was still the cheapest for a "basic staples basket" - the only basket for which ALDI's products are featured because of its small product range.
GROCERYchoice publishes the average prices of grocery "basket" categories at supermarket chains across Australia, using 500 products typically bought by Australian households.
The baskets include meat and seafood, fruit and vegetables, dairy, breads and cereals, drinks and other snacks, general groceries, household and personal care.
The price of the basic staples basket is calculated from a range of staple products from the other baskets.
To stop price manipulation, individual product prices are kept confidential and the products surveyed are rotated.
