Give a geographical explanation of the distribution of off-shore oil reserves of the world. How are they different from the on-shore occurrences of oil reserves? (Answer in 250 words)

Oil accumulates where organic-rich sediments mature in suitable geological basins and hydrocarbons migrate into porous reservoirs sealed by impermeable strata. These conditions occur on land and beneath continental margins.

Offshore distribution

• Major reserves lie on broad passive continental shelves and sedimentary basins, including the Persian Gulf, Gulf of Mexico, North Sea and offshore West Africa.
• River-borne sediments, high organic productivity, rapid burial and structural traps favour petroleum systems.
• Deep-water provinces such as Brazil’s pre-salt basin reflect thick sedimentary sequences and effective salt seals.
• In India, Mumbai High and the Krishna–Godavari basin are important offshore regions.

Comparison with onshore occurrences

• Onshore fields occur in sedimentary basins such as the Middle East, West Siberia, Assam and the Cambay basin; offshore fields extend beneath seabeds and continental margins.
• Offshore exploration requires seismic surveys, platforms, subsea wells, pipelines and specialised logistics; capital intensity and operating risk are higher.
• Onshore infrastructure and maintenance are generally cheaper, though terrain, conflict, land acquisition and ecological impacts may be significant.

Environmental context

Offshore spills threaten fisheries, mangroves and tourism, while onshore extraction can fragment habitats and contaminate groundwater. Reserve distribution is geological, but exploitation depends on technology, price, geopolitics, safety regulation and the energy transition.

Keywords: sedimentary basin, continental shelf, source rock, reservoir, seal, Mumbai High, pre-salt.