Isramco announced Sunday that "extremely significant" reserves of natural gas have been discovered at its Tamar 1 offshore drill site 90 kilometers west of Haifa.
The natural gas reserve is the largest ever discovered in Israel - three times bigger than that of the "Yam Thetis" consortium and worth $15 billion.
"Subject to receipt of further data from the drill site, the estimated reserves of natural gas are likely even to increase," the company said in a statement.
Tamar is a joint venture between the U.S. company Noble Energy (36%), Isramco (28.9%), Delek Drilling and Avner Oil and Gas Exploration. It is named after the grand-daughter of geologist Yossi Langotsky.
Drilling is difficult: the sea floor is 1,700 meters below the surface of the water and under the sand is a 1,400-meter thick stratum of salt. The drill at the Tamar 1 permit site reaches 5,000 meters below sea level.
Tel Aviv stocks rose on the back of the announcement. Isramco shares rose 123 percent, the Delek Group was up 57 percent, and Avner was up 45 percent.