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DUBAI, Dec 17 (Reuters) - BP BP.L became the second Western oil major to renew a 40-year onshore concession in Abu Dhabi on Saturday after almost two years of negotiations to improve terms to help operate the United Arab Emirates' biggest oilfields.

The British oil company signed an agreement with state-run Abu Dhabi National Oil Company (ADNOC) giving it a 10 percent stake in the Abu Dhabi Company for Onshore Petroleum Operations (ADCO), which operates the concession.

"BP becomes a 10 percent shareholder in ADCO," ADNOC said in a statement. "The agreement includes BP becoming asset leader for the Bab asset group within the concession."

The ADCO concession, including the Bab, Bu Hasa, Shah and Asab fields, has total resources of between 20-30 billion barrels of oil equivalent over the term of the concession. The fields produce 1.6 million barrels per day (bpd) and are expected to reach 1.8 million bpd from 2017.

Total TOTF.PA was the first oil major to renew the concession, securing a 10 percent stake in January last year and putting its peers under pressure to improve terms after ADNOC said the French company made the best offer.

Asian and other Western oil firms also bid for stakes after a deal with major oil companies in the concession first granted in the 1970s expired in January 2014.

Total and BP had both held 9.5 percent equity stakes in the ADCO concession since the 1970s. Shell RDSa.L and Exxon XOM.N were also partners in the old concession.

Since then other Asian energy companies were granted smaller stakes. INPEX Corporation 1605.T of Japan, and GS Energy of South Korea GSHOLE.UL received 5 percent and 3 percent stakes respectively.

ADNOC said it "continues to look for partners to take up the remaining 12 percent stake of the 40 percent earmarked for foreign partners."

As part of the deal, BP said it would issue 392,920,353 of new ordinary shares to be held on behalf of Abu Dhabi's government at a price of 4.47 pounds ($5.58) per ordinary share.

This represents approximately 2 percent of BP's issued share capital, excluding treasury shares. ($1 = 0.8004 pounds)

(Reporting by Rania El Gamal and Dmitry Zhdannikov; Writing by Sami Aboudi; Editing by Jason Neely and Helen Popper) ((Sami.Aboudi@thomsonreuters.com; +97143918301;))