The lack of variation in grocery prices is in "the realm of remarkable coincidence", according to the Director of Consumer Affairs, Ms Carmel Foley.
Ms Foley said she was concerned there might be underlying anti-competitive elements in supermarket retailing. She was commenting after the publication of the results of the second in a series of four monthly surveys commissioned by the Office of the Director of Consumer Affairs (ODCA).
She is forwarding the results of the surveys to date to the Competition Authority for its consideration.
The survey was conducted at supermarkets and large and medium-sized stores in Dublin, Cork, Limerick, Dundalk, Galway, Athlone, Sligo and Carlow/Kilkenny.
It found very little price difference between Tesco, Dunnes Stores and Superquinn throughout the State. Dunnes Stores and Tesco match each other's prices so closely in many areas that there is no variation, especially on staple items.
Spar, Centra and Londis matched the others closely on certain items, such as butter and sausages, but were more expensive for milk, bread, dry grocery goods, baby and bathroom products and "luxury items" such as cans of cola.
SuperValu prices tended to hover between Dunnes Stores/Tesco prices and prices in convenience stores.
The survey of 36 branded items was carried out by the Consumers' Association of Ireland on behalf of the ODCA. The chief executive of the association, Mr Dermott Jewell, said the fact that prices continued to mirror each other again seemed to indicate that the main supermarkets were watching each other closely and there was no real competition.
The marketing director of Superquinn, Mr Eamonn Quinn, interpreted the results differently. "The fact that there is so little variation in prices proves that there is competition," he said. "There is such a competitive market that everybody is looking at what everybody else is doing and if they see a significant price difference they will adjust it accordingly."
The director of corporate affairs at Tesco, Mr Dermot Breen, said there was a high level of competition in the Irish grocery market. "The survey only incorporates a selection of branded products that would be closely watched and marked.
"A lot of the major price reductions we have introduced in the last couple of months have been our own-label products, where there is greater flexibility in pricing."
Dunnes Stores declined to comment.