UPDATE 1-Conoco, ADNOC sign long-awaited Abu Dhabi gas deal

(Adds details, background)

By Daliah Merzaban

DUBAI, July 8 (Reuters) - ConocoPhillips (COP.N) and Abu Dhabi National Oil Co (ADNOC) signed a long-expected deal on Tuesday to develop sour gas reserves in the United Arab Emirates for a cost that could exceed $10 billion.

The partners did not release the expected project cost after signing the deal, saying only they would "jointly share" any investments in developing sour gas reservoirs within the onshore Shah field.

An ADNOC spokesman declined to comment on the investment costs related to the project.

Costs of the project have escalated, as they have worldwide in the energy sector as producers strain to bring new capacity online to meet rising demand.

"Completion of final joint venture agreements ... is expected by year-end," ADNOC and Conoco said in a statement.

The sour gas deal is one of the largest upstream projects in the past year open to international companies competing for limited access to the Middle East's oil and gas fields.

Saudi Arabia, home to the world's largest oil reserves, keeps its oilfields closed to international firms.