Analysts estimate that Ulster Bank is worth around pounds 2bn. Irish Life and Bank of Ireland said they were considering a joint bid while Allied Irish Banks, the nation's largest bank, said it was examining Ulster Bank by itself.
NatWest plans to sell the bank as part of its defence against a pounds 22bn hostile bid from Bank of Scotland. NatWest has set a deadline of Wednesday for all bids.
"I quite like the chances of the Irish Life and Bank of Ireland plan because they can get around any monopolies problems," said Ian Poulter, an analyst at Williams de Broe.
If the joint bid succeeds, Ulster Bank would be split so that Bank of Ireland would take Ulster Bank's business in Northern Ireland and Irish Life & Permanent would take everything in the Republic of Ireland.
The joint Bank of Ireland/ Irish Life offer or an independent bid from Allied Irish Banks are likely to be higher than others because they can achieve savings by cutting administrative staff.
Allied Irish said it would examine Ulster Bank, but declined to say whether it would submit an offer. "Because of its quality and size, we certainly will be taking a look at Ulster Bank," said a spokesman.
Bank of Ireland spokesman David Holden said his company has said it wants to expand in Northern Ireland.
Irish Life & Permanent was formed this year by the merger of the country's top life insurer and mortgage lender and has said it would like to increase its branch network.
Ulster Bank made about 60 per cent of its pounds 113m profit in 1998 in the Republic, where it has 103 branches.Reuse content