Subsidiaries of conglomerate Israel Corp are to buy Egyptian natural gas in a 20-year deal worth between $5 billion to $10 billion, adding to the uncertainty over the future of Israel's own Tamar gas development.

The total quantity covered in the contracts with East Mediterranean Gas (EMG) is set at 1.4 billion cubic meters (bcm), annually, for 20 years. The buyers do though have the option to increase the amount up to 2.9 bcm annually, one EMG shareholder said on Monday.

EMG, which sells Egyptian gas to Israel, competes with gas produced off of Israel's shores by various groups led by Texas-based Noble Energy.

A source in the Egyptian Holding Company for Gas (EHG) who spoke to Ahram Online on condition of anonymity said that EHG is not part of "any" deal with Israel. EHG, a public company, signed a deal with EMG in 2005 to supply it with certain quantities of gas. "There was no increase in this quantity since," he added. In reference to the new EMG deal with Israel, the source explained that EMG is "free" to supply any of its clients with any amount of gas.

Noble Chairman and CEO Charles Davidson said at a conference in Tel Aviv on Sunday that a proposal to raise the Israeli government's tax on gas discoveries creates uncertainty around the schedule and financing of the Tamar prospect, the world's largest gas find in 2009.

Infrastructure Minister Uzi Landau said at the conference that it was crucial to develop Tamar on time because Mari-B, the only Israeli gas field in production, would be depleted by 2013, leaving Israel dependent on foreign gas.

According to a statement from the Israeli partners in Tamar, Landau sent Prime Minister Benjamin Netanyahu a letter stating that a central potential customer of the Tamar project was about to decide whether to purchase gas from EMG and he urged Netanyahu to intervene to prevent delays in the development of Tamar.