The companies cited the best estimate for unrisked gross prospective gas resources provided by Texas-based consultants Netherland, Sewell & Associates.
They said they have not yet made a decision as to whether they will develop the reservoirs in the Tamar Southwest prospect.
Texas-based Noble Energy owns 36 percent of Tamar, while Delek Drilling and Avner Oil Exploration , both subsidiaries of Delek Group, hold 15.625 percent each.
Isramco Negev holds 28.75 percent and Dor 4 percent.
Two of the world's largest offshore fields from the past decade were found in Israeli waters. The first of the fields, Tamar, with an estimated 10 tcf of gas, came online in late March.