Grocery prices at Coles and Woolworths are almost identical while Aldi customers have emerged as big savers, research reveals.
But shopping across all three supermarkets could be the best way to reduce household costs.
An average basket of 14 common household items was $68.70 at Woolworths and $69.91 at Coles - a difference of $1.21 - data from consumer group Choice on supermarket prices found.
With specials, Coles came out on top at $66.22 while Woolworths prices sat at $68.37 - a $2.15 split that pales in comparison to Aldi, whose groceries basket cost $50.79 regardless of discounts.
The Choice report also found slight changes in the cost of groceries in the June quarter, compared with its initial report for the March quarter.
Woolworths' basket with specials was $3.44 more expensive; at Coles the prices came down $2.30 and Aldi's items were 72 cents cheaper.
Assistant Competition Minister Andrew Leigh said the falling prices indicated competition was working and suggested Australians were shopping around.
"That is good for consumers but it's also good for the people who don't shop around because it puts competitive pressure on the supermarkets to offer the best deal," he said in Canberra on Thursday.
However, the Australian Retailers Association claimed the Choice report lacked transparency because the consumer advocacy group hadn't specifically named the products it analysed.
The association's CEO Paul Zahra argued the report could be comparing premium brands at Coles and Woolworths to Aldi's private label options.
He noted that 14 items amounted to a "very narrow basket" given supermarkets offered thousands of products.
"This is not a fair or useful comparison for customers," he said.
Choice selects products to ensure it can make fair comparisons, often sticking to basic items with limited differences across brands and products from both national and house brands.
The goods in its basket included apples, carrots, Weet-Bix, sliced white bread, flour, penne pasta, sugar, tea bags, tasty cheese, milk, frozen peas, beef mince and butter.
Choice also tries to ensure the products are comparable by selecting goods of similar size and quality.
Mr Zahra maintained it was important for Australians to check prices themselves, suggesting they used apps that allow them to compare costs.
"It's important that customers - if they're working to a budget - that they do their homework," he told Nine's Today show.
"Retailers, by nature, will always try to offer value."
The findings come in the same week the consumer watchdog launched legal action against Coles and Woolworths over allegations the retailers mislead consumers about product discounts.
The Australian Competition and Consumer Commission accused them of increasing prices for a brief period before lowering them and moving the products to promotions on sale - at costs often still higher than the initial price.
Choice chief executive Ashley de Silva said specials made a large difference at the checkout.
"Choice has previously found supermarket labels are often confusing, making it difficult to tell if there is a true discount on offer or not," he said.
"(The report) highlights the importance of clear, simple labelling that leaves the customer in no doubt about whether a product is actually on special."
The Choice reports, which are produced quarterly, are funded by the federal government in response to consumer concerns about price gouging.
A Woolworths spokesperson said its products were competitive with prices at discount retailers and its range was 30 per cent cheaper on average than the brands included in the Choice report.
"We remain focused on delivering value for customers," they said.
