Washington, July 27 - Scientists have found that petroleum can be formed under the very high pressure and temperature conditions found deep within the earth. The finding potentially multiplies underground oil deposits manifold.

The oil and gas that fuel our homes and cars started out as living organisms that died, were compressed, and heated under heavy layers of sediments in the earth's crust. Scientists have debated for years whether some of these hydrocarbons could also have been created deeper in the earth and formed without organic matter.

Now scientists from Carnegie Institution's Geophysical Lab have found that ethane and heavier hydrocarbons can be synthesised under the pressure-temperature conditions of the upper mantle -- the layer of earth under the crust and on top of the core.

Methane is the main constituent of natural gas while ethane is used as a petrochemical feedstock.

The scientists first subjected methane to pressures exceeding 20,000 times the atmospheric pressure at sea level and temperatures ranging from 700 to over 1,200 degrees Celsius.