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 The petroleum thus formed got trapped between the layers of impervious rocks (non-porous),

forming an oil deposit. Petroleum is lighter than water, so it floats over water.

Occurrence and Extraction of Petroleum:

 Petroleum is found trapped between the layers of impervious rocks. Petroleum being lighter

than water floats over it. Petroleum oil deposits are generally mixed with water, salt and earth

particles. Natural gas occurs above the petroleum oil.
 Petroleum is extracted by drilling holes also known as oil wells in the earth’s crust, where the

presence of oil has been predicted by survey.
 The oil wells are drilled by using drillings rigs.

 The petroleum and the natural gas are present under the earth surface under high pressure.
 So, when an oil well is drilled through rocks, natural gas comes out first with great pressure

followed by the petroleum oil. After the gas pressure has subsided, petroleum is pumped out

of the oil well.
 Earlier, drilling of oil wells for getting petroleum was done only on land, but later using new

techniques now oil wells are now also drilled under the sea for extraction of petroleum oil.

 The world’s first oil well was drilled in Pennsylvania, USA, in 1859. Eight years later in 1867oil
was struck at Makum in Assam. In India, petroleum oil is found in Assam, Gujarat, and

Mumbai High and in the river basins of Godavari and Krishna.

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