The Natuna D-Alpha Block is located in the Natuna Sea in Indonesian waters northwest of Kalimantan. ESSO Exploration and Production Natuna Inc. , an affiliate of EXXON Corporation, acquired the 4,165 square kilometre block on January 8, 1980, holding a 50 percent working interest with PERTAMINA. The block has been part of a much larger block covering the East and West Natuna area operated by AGIP for a group Composed of AGIP, Phillips Petroleum Inc. , and Tenneco, each with a 33 1/3 percent interest. Four wells were drilled by the group. The discovery well AL-IX spudded in September 1973 and drilled to a total depth of 4603 m(15,102 feet ) in 470 feet of water. The larger AGIP, et al Block" A" was relinquished in 1977 to PERTAMINA, which subsequently offered the 4,165 square kilometres Natuna D-Alpha Block for bidding with an August 1, 1979 tender date.