Leviathan was the world's largest offshore gas discovery of the decade when Texas-based Noble Energy and its Israeli partners found the deposit about 80 miles (130 km) west of the Israeli port of Haifa in 2010.
The group initially said the field held about 16 tcf, but has since lifted its estimate incrementally. Ratio Oil Exploration, which has a 15 percent stake in the field, presented a new evaluation made by Texas-based consultants Netherland, Sewell & Associates that listed a best estimate of 18.9 tcf.
Noble has a 39.66 percent share and the Delek Group holds 45.34 percent through two subsidiaries.
The Leviathan partners announced in December they will sell a 30 percent stake to Australia's Woodside Petroleum for $1.25 billion. The deal has not been finalised.