When the rocks originally formed under the sea, not only oil was trapped but also sea-water. Because oil is lighter than water it usually lies above it in the rock.Above the oil are the lightest hydrocarbons forming natural gas.Others think that oil may have formed relatively rapidly after the organisms were trapped in the sediments and that heat or pressure was not necessary to the process.
It is of less commercial significance because it yields little motor-oil during distillation.
India has total reserves (proved and indicated) of 757% million metric tonnes of crude oil and 1241 billion cubic metres of natural gas as on 1.4.2011.
Petroleum, the mineral which is in the greatest demand in modern industry, supplies half the world’s energy requirements.
kms form marine basins of Mesozoic and Tertiary times.
India’s offshore areas have Mesozoic and Tertiary rocks of marine origin spread over 2.5 lakh km up to 200 metres,the probability of oil occurrences is rated high in these rocks (divided into 10 basins), particularly the Cambay region where oil was discovered in Bombay High in 1974.