Why is petroleum found only in off-shore or coastal areas?

This is not true. A lot of reserves are onshore around the globe. From 1965 to till now 57% of the production has come from onshore reserves. In India alone Barmer, Assam and Ahmedabad are onshore reserves. In China Daqing & Tarin Basin are inland among others. Main oil production areas in Russia are all inland. read more

Offshore and coastal are lower regions so you could expect a flow downwards of whatever can flow and then getting accumulated there. Hence a reasonable amount has already been proven offshore and some are still to be found. But it is not true that petroleum is found only offshore and in coastal. read more

Natural gas is usually found near petroleum. Many factors can affect oil production, such as civil unrest, national or international politics, adherence to quotas, oil prices, oil demand, new discoveries and technology development or application. read more