Abu Dhabi National Oil Company (Adnoc) said on Monday it had granted Japan's Inpex Corp a 5 per cent stake in a new 40-year concession, making it the first Asian firm to help operate the UAE's biggest oilfields after decades-long partnerships with Western majors.

Nine Asian and Western companies bid for stakes in the Abu Dhabi Company for Onshore Oil Operations (Adco) concession after a deal with the Western majors dating back to the 1970s expired in January 2014.

The fields produce 1.6 million barrels per day (bpd) and output is expected to rise to 1.8 million from 2017.

Total became the first oil major to renew the concession, putting peers under pressure to improve terms after the local partner said the French firm made the best offer.

Last week, Adnoc's director general said there was no deadline for awarding further stakes in the concession, suggesting Abu Dhabi was in no rush to make a decision about other bidders in the tender.

The Inpex concession gives Japan, which imports almost all of its oil and is the fourth-biggest importer, the ability to procure oil without passing through the chokepoint of the Strait of Hormuz at the entrance to the Persian Gulf, Minister of Economy, Trade and Industry Yoichi Miyazawa told reporters.

"This is an epoch-making event and this pact will contribute greatly to Japan's stable procurement of oil," Miyazawa said.

It is the first major stake in an oil concession Japan has obtained since 2009. Japan holds stakes in oilfields producing 610,000 bpd and the ADCO concession will boost the figure by 15 per cent when production is expanded to 1.8 million bpd.

Inpex did not disclose the value of the deal due to a confidentiality agreement, but Japanese public broadcaster NHK said earlier it was expected to be worth $1.1 billion.

Other bidders for the concessions include Occidental Petroleum Corp, Italy's ENI, China National Petroleum Corp, Norway's Statoil and Korea National Oil Corp.

The concession signed with Total was effective from Jan. 1, 2015, and covers Abu Dhabi's 15 principal onshore oilfields that represent more than half of the Gulf emirate's production.

Four oil majors -- ExxonMobil, Royal Dutch Shell , Total and BP -- had each held 9.5 per cent equity stakes in the ADCO concession since the 1970s.

After the deal expired last year, state-run Adnoc took 100 per cent of the concession as political leaders in Abu Dhabi weighed up whether to bring in Asian firms or stick with old partners, industry and diplomatic sources said.

Shell and BP have also put in new bids, while Exxon has decided against bidding, sources have told Reuters. – Reuters