Industri Energi and Safe, representing some 87 percent of Norwegian oil workers, said the outcome of the talks was disappointing, but added they had nevertheless accepted it as they did not have the right to go on strike this year due to a clause in last year's agreement.

Lederne, a third union representing some 13 percent of Norwegian oil and gas workers or about 1,000 people, does have the right to go on strike, and said it had rejected the oil firms' offer.

Under Norwegian law, the talks involving Lederne will now proceed to a state mediator, which must be conducted before any strike is allowed.

Norway is western Europe's top oil and gas producer with daily output in April of around 2.1 million barrels of oil, condensate and natural gas liquids, as well as natural gas corresponding to about 1.7 million barrels of oil equivalent.

Top operators offshore Norway include, among others, Statoil (>> Statoil ASA), Aker BP (>> Aker BP ASA), Total (>> Total), Exxon Mobil (>> Exxon Mobil Corporation), Shell and Centrica (>> Centrica PLC).

(Reporting by Oslo newsroom; Editing by Mark Potter)