Several offshore wells were drilled in the Mediterranean Sea during the 1970's to 1990's in shallow water, 10 to 20 km west of the Israeli coast. No commercial success was reached although significant, light oil shows were discovered in the Yam-2, and Yam-yaffo-1 wells. In June 1999, the Tethys Sea Partnership announced the discovery of gas in Noa-1, drilled 40 km west of the coastal town of Ashkelon. The Noa field was the first, significant natural gas reservoir found offshore Israel. In February 2000, another gas reservoir, the Mari-B field, was found southeast of the Noa field. At the time of discovery Mari-B contained 45 BCM of gas in place. In 2004, commercial gas production began from the Mari-B field through a production platform that was built 25 km west of Ashkelon and a gas receiving terminal near the port of Ashdod. Almost all the gas produced from the field was used by the Israel Electric Company to operate some of its power units, which were converted from diesel and coal to natural gas utilization.
Following Noa and Mari-B discoveries in the southeastern part of the Israeli Exclusive Economic Zone (EEZ), exploration efforts began to accelerate. In the early 2000's new, regional 2D and 3D seismic data was acquired throughout the offshore. Exploration licenses were granted to several oil companies including Noble Energy, Avner and Delek Drilling the Tethys Sea partners that discovered Noa and Marie-B. In January 2009 Noble Energy and its partners announced the discovery of gas bearing sands in the Tamar-1 well, located in 1600 m water depth, 90 km west of Haifa in the northern part of the EEZ. The Tamar structure was estimated to contain at the time of discovery some 240 BCM of recoverable gas reserves, an amount that can provide for Israel's domestic consumption of gas for several decades. Later this year the same partnership discovered natural gas in the smaller Dalit field, southeast of Tamar, with an estimated amount of 8 BCM of gas.
In June 2010 a partnership headed by Noble Energy, Delek Drillings and Ratio Oil and Gas announced the largest discovery made so far in the Israeli economic water. The giant, Leviathan structure located in deep water, 30 km west of Tamar, was found to contain the same gas bearing Tamar Sands. Initial analysis indicated to recoverable reserves of 450 BCM of gas in the Leviathan field, which was later increased to 500 BCM following the drilling of several appraisal wells. The giant Leviathan Field was the largest discovery world-wide during the first decade of the century. Exploration activity in the northern part of the Israeli EEZ continued through 2011 to 2013 with more success. Additional amounts of gas were discovered in the Karish, Tanin, Dolphin, Tamar SW and Aphrodita-Ishai fields.
