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?

Offshore fields supply roughly 30% of world oil. Their distribution is not random — it follows the geology of continental margins and ancient seas.

Geographical Explanation of the Distribution

• Passive continental margins with kilometres-thick marine sediments, where organic-rich source rocks matured under slow subsidence: the Gulf of Mexico, Brazil's pre-salt Santos–Campos basins, and the West African margin off Nigeria and Angola.
• Shallow epicontinental seas over the former Tethys: the Persian Gulf — including Safaniya, the world's largest offshore field — concentrates giant accumulations in gentle anticlinal traps.
• Rifted and graben basins: the North Sea (Brent, Ekofisk) and India's Bombay High on the western continental shelf.
• Major deltas prograding seaward supply both sediment and traps: the Niger, Mississippi, Mahakam and Krishna-Godavari.
• Structural traps — salt domes in the Gulf of Mexico, rollover anticlines in deltas — plus Arctic shelves (Barents, Kara) as a frontier province.

Contrast with On-shore Occurrences

• Geology: offshore accumulations lie mainly in younger Cretaceous–Tertiary marine shelf sediments; classic onshore giants occupy older platform and foreland basins — Ghawar in Saudi Arabia, the Permian Basin, West Siberia, Assam.
• Technology and cost: offshore production needs platforms, subsea completions and FPSOs; deepwater wells cost multiples of onshore wells, so breakeven prices are higher.
• Risk profile: cyclones, blowouts and marine spills (Deepwater Horizon, 2010) offshore, versus land acquisition and local displacement onshore.
• Geopolitics: offshore reserves generate EEZ and maritime delimitation disputes (South China Sea, Eastern Mediterranean) governed by UNCLOS; onshore reserves raise federal revenue-sharing questions.
• Evacuation: offshore crude moves by subsea pipeline and tanker; onshore fields link directly to pipeline and rail grids.

For India — Bombay High and the KG deepwater block KG-DWN-98/2 — offshore holds the main upside against an import dependence above 85%, making shelf exploration under the Open Acreage Licensing Policy strategically vital.