Sainsbury's and Asda will be able to increase their Northern Ireland customer base "considerably" if their merger gets the go-ahead, it's been claimed.
Research organisation Kantar Worldpanel commented as its latest analysis of the grocery market found German discounter Lidl had grown its sales by 5.7% - the fastest sales growth of all the major players.
But Tesco remained the number one grocer in Northern Ireland, growing sales by 2.6% over the last 12 months, with a market share of 35.2%. And shoppers were making one extra trip to Tesco a year, increasing their average spend by £54.
Sainsbury's was behind Tesco with a share of 17.3%, with Asda in third place with 17.1% of the market.
Lidl's market share was 5.6%, and its shoppers were spending an extra £1.40 per trip.
Kantar Worldpanel said that even if Asda and Sainsbury's combined, their 34.4% market share would still be dwarfed by Tesco.
Tesco has around 50 stores in Northern Ireland, while Sainsbury's has 14 and Asda 17. Lidl has 39 smaller-format units.
The varying customer base of Asda and Sainsbury's in Northern Ireland meant there was some logic to a tie-in, Kantar added.
Douglas Faughnan, consumer insight director at Kantar Worldpanel, said: "The Northern Ireland grocery market is set for its biggest shake up in a generation if the merger goes ahead.
"By joining forces, Sainsbury's and Asda would create a wider shopper base than either has individually.
"Over the past 12 months 48% of Sainsbury's sales went to empty nesters and the retired, in contrast to only a third at Asda.
"Meanwhile, families preferred the Walmart-owned retailer, accounting for 49% of sales, versus 30% at Sainsbury's.
"Sainsbury's appeals to more affluent and city-based customers, with more than half of its sales coming from Greater Belfast this year compared to Asda's third."
A retail expert has warned that job losses and store closures are inevitable if the merger goes ahead.
Retail analyst Donald McFetridge said the Competition and Markets Authority (CMA) watchdog will insist on closures where monopolies could exist if the two join forces.
Meanwhile, Lidl has joined fellow German discounter Aldi in firing the latest salvo in the UK's supermarket price war, pledging to keep prices lower than rivals in response to the proposed Sainsbury's and Asda merger.
Sainsbury's last week promised to bring down prices on everyday items by 10% after it completes its £12bn merger with Asda. Chief executive Mike Coupe said he would put pressure on large suppliers and pass on cost savings to consumers.
Walmart's significant buying power will also give Sainsbury's an advantage in general merchandise, he said.
However, the German discounters have responded aggressively to Sainsbury's price promise, saying they will remain the cheapest option on the high street.