A major strike would add a new dimension to the regional energy boom that will transform the economies of Israel and nearby Cyprus, and could do the same for Lebanon, the Palestinians and their quest for an independent state, and even a post-civil war Syria.
Leviathan is Israel's largest gas field, containing an estimated 19 trillion cubic feet of gas, with Noble the major stakeholder along with leading Israeli partner Delek Group.
To get to the oil-bearing strata that lie beneath Leviathan's gas deposits, Noble will have to drill the Jewish state's deepest well, 31,200 feet below the Mediterranean seabed.
If it hits pay dirt, the oil would be enough for Israel's current requirements for 15 years.
On top of the estimated 25 trillion cubic feet of gas so far discovered off Israel -- which the government estimates could earn $20 billion over the next decade or so -- that amount of oil would mean Israel, the Middle East's third largest economy, could halt imports that cost $10 billion a year.
Gas production began March 30 from Israel's Tamar field, which contains an estimated 8 tcf of gas and is also owned and operated by Noble-Delek. Leviathan's gas is expected to start flowing in 2016.
Noble expects its oil exploration program, with an anticipated cost of more than $120 million for the Leviathan gas strike, will get under way toward the end of the year, after the arrival of a drilling vessel currently being built in South Korea.
The company, based in Houston, estimates its chances of success at 25 percent.
If the anticipated volume of oil is found, it will likely post swifter returns than the gas.
Where gas requires costly pipelines or liquefaction plants so it can be transported by sea to countries that have plants to turn the gas back to its original form, oil just needs to be pumped into tankers and can be shipped anywhere in the world.
"The economic impact on Israel would be far greater than that of natural gas," said David Wurmser, director of the Delphi Global Analysis Group. "Finding the oil would mean big money for the Israeli companies and the government."
A major oil discovery off Israel would galvanize the regional energy boom. Israel is by far the most advanced. Cyprus has found gas in its Aphrodite field off the island's southern coast and expects more big strikes.
Lebanon is still carrying out seismic tests but claims it has an estimated 25 tcf so far, with more expected. Gas has been found off the Gaza Strip, but no drilling has taken place because of Israel objections.
Syria's reserves are not known, and won't be until its 2 1/2-year-old civil war ends.
The U.S. Geological Survey reported in 2010 the Levant Basin, covering all these territories, contains at least 122 tcf of gas and 1.7 billion barrels of oil.
Noble-Delek aren't the only ones seeking oil offshore. Israel's Shemen Oil and Gas Exploration, has been drilling in the Yam-3 block since December 2012, including a halt of several weeks because of technical snags.
Shemen Chief Executive Officer Yossi Levy first drilled for oil off Israel's southern port of Ashkelon in 1988 when he headed the state-run Naphtha Co. The project -- which relied on the secret participation of U.S. oil major Occidental Petroleum at a time when the Arab boycott of the Jewish state was at its height -- folded in 1990 without a major strike.
A geological study commissioned by Shemen estimates there's at least 120 million barrels of oil in Yam-3. Levy says that could bring in $20 billion-$24 billion in licenses. The results should be known in August.
Israel's growing energy wealth may well intensify the country's security problems at a time when the Arab world is in turmoil, with Egypt again in ferment, Syria locked in a civil war that's killed 93,000 people, and Jordan looking increasingly vulnerable.
All this will mean a major effort by Israel to build up naval forces to defend its oil and gas infrastructure from its regional adversaries.