Leading consumer advocacy group CHOICE conducted mystery shops at the major supermarket chains across all states and territories in January as part of its cost surveys.

It found "a few trends" in the first year of its quarterly basket survey, including Coles and Woolworths are closely matched on price and that Aldi continues to be cheapest.

Based off 14 commonly bought items and including specials, Aldi came out on top for the fourth time as the lowest at $51.36 for a basket, compared to $51.51 in March 2024.

Coles ranked second at $66.84, down from $68.52 in March 2024, followed by Woolies on $67.34, an increase from $64.93 and IGA $74.90, compared to $78.95 in June.

CHOICE flagged despite Woolworths' price increase by 1.5 per cent, it was lower than its September high of $69.17. IGA was not included in the March 2024 survey.

Coles' basket cost lowered by 2.1 per cent, while Aldi decreased by 0.3 per cent.

The basket consisted of 14 popular items, 12 were packaged products which were national brands or supermarket/budget brands such as mince and milk, and two fresh fruit and vegetable options of apples and carrots.

The other products were butter, bread, peas, Weetbix, penne pasta, diced tomatoes, block of cheese, flour, tea bags and sugar.

The results came from undercover shops at a total of 104 supermarkets, including 27 Woolies, 27 Coles, 23 Aldi and 27 IGA stores across 27 locations across Australia.

CHOICE noted the slow widening of overall basket cost between the two major supermarkets of Coles and Woolworths, growing from 75 cents last survey to $1.79.

"It's still not a huge difference, but it certainly has shifted in that time," Ashley de Silva, the CEO of the leading consumer advocacy group said.

"We have always reported each quarter the gaps between them, but I think this is the most pronounced that that gap has been."

It means shoppers could be forking out more than $90 a year if shopping weekly.

In a statement, a Woolworths spokesperson said analysts had pointed out "gaps" in basket comparisons "which don't look at the lowest priced product from each retailer".

"When like-for-like products are compared our prices are much closer to ALDI’s," it said.

"Our Woolworths own brand range of products are on average 30 per cent cheaper than mainstream national brands, which we know CHOICE has used in this basket."

The report provides minimal relief for families who continue to do it tough with cost of living, with grocery prices one of the biggest concerns for households.

Just last week the Australian Competition and Consumer Commission (ACCC) could not determine if price gouging was happening at supermarkets.

However, it notes Australia's supermarket sector is one of the most profitable in the world.

Woolworths' profits dropped 21 per cent to $739 million in the six months to January due to industrial action by its workers last year and as shoppers hunt for discounts.

While Coles' net profit dropped three per cent to $576m in the same period.

The ACCC has made 20 recommendations to the federal government including mandating stores to publish all grocery prices on respective websites.

It also pointed to improvement on transparency around pricing, promotions and loyalty programs to inform shoppers if they are receiving a good deal.

“Through clearer sales tickets and promotions, consumers will be better placed to make more informed decisions about what products offer the best value for them at the checkout," ACCC deputy chair Mick Keogh said in the report.

Consumers also raised concerns about "shrinkflation" - when a product's price increases but size decreases, and the cost remains the same or rises.

The ACCC is recommending supermarkets advise shoppers when it happens.

"This information would, at a minimum, be required to be published in proximity to the product ticket on shelves, and on the webpage for the product," the report said.