QUES . 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.15 marks. UPSC MAINS 2025. GS PAPER 1
HINTS:
Offshore oil reserves are petroleum deposits located beneath the seabed, extracted using offshore drilling techniques, and are becoming increasingly vital as land-based reserves deplete. Key regions for offshore reserves include the Persian Gulf, North Sea, Gulf of Mexico, West Africa, and the Asia-Pacific.
Distribution of Off-shore Oil Reserves of the World
(a) Persian Gulf
Offshore fields in Saudi Arabia, Iran, UAE, Qatar and Kuwait. Safaniya Oil Field in Saudi Arabia is the largest conventional offshore field by both proved reserve size and production capacity.
Reason for vast oil reserves in Persian Gulf:
Ancient shallow seas with abundant organic matter, burial under heat and pressure to form oil, and large structural traps like anticlines formed by plate tectonics (collision of the Arabian and Eurasian plates) to hold the oil. The abundance of high-quality reservoir rocks like carbonates and effective sealing rocks, along with favorable sedimentary conditions, trapped enormous quantities of oil and gas, creating the region’s rich petroleum endowment.
(b) North Sea
Offshore reserves of UK, Norway (Johan Sverdrup field) and Denmark.
Reason for oil reserves in North Sea:
The North Sea basin contains thick layers of shale and other organic-rich rocks from the Jurassic and Cretaceous periods, which are crucial for oil formation. Over millions of years, the organic material in these sediments was buried deeper, subjected to intense heat and pressure, and chemically transformed into oil and gas.
(c) West Africa (Gulf of Guinea)
Nigeria, Angola, Ghana, etc.
Reason for oil reserves in Gulf of Guinea:
The Gulf of Guinea, a major oil-producing region, has extensive geological formations conducive to hydrocarbon formation and accumulation. The opening of the South Atlantic Ocean during the Lower Cretaceous period, created a favorable environment for the accumulation of hydrocarbons.
(d) South America
Countries like Brazil and Guyana have discovered massive oil reserves in deepwater offshore fields. These pre-salt fields are rich in high-quality low-sulfur oil.
(e) North America (Gulf of Mexico)
Major oil-producing region of USA and Mexico.
Alaskan offshore, including both Beaufort and Chukchi Seas, hold vast but largely unproven oil and gas resources.
Reason for oil reserves in Gulf of Mexico:
The constant supply of coarse-grained and fine-grained sediments mainly through erosion processes that take place on the land of North America (sediments are mostly carried away via rivers). Also the salt formations in the Gulf has supported in accumulation of oil.
(f) South & Southeast Asia
Off-shore reserves are mostly in India, Vietnam, Brunei, Malaysia and Indonesia. As of May 2025, Mumbai High’s output accounted for about 35% of India’s domestic oil production.
(g) East Asia
The South China Sea is believed to hold large quantities of oil and natural gas.
(h) Caspian Sea
Caspian Sea holds significant oil reserves. Azerbaijan and Kazakhstan are the top producers of oil from offshore Caspian fields. For example, Kashagan field (Kazakhstan) in the North Caspian.
(i) Arctic’s offshore areas
The Arctic is estimated to hold a substantial portion of the world’s undiscovered petroleum resources. Receding sea ice is increasingly making more of the Arctic’s offshore areas accessible for exploration and extraction.
Difference Between Off-shore and On-shore Oil Reserves
Location and Formation
Offshore
In continental shelves and marine sedimentary basins beneath seabed.
Onshore
Land-based ancient sedimentary basins beneath land (deserts, plains,etc.) surface.
Distribution
Offshore
Persian Gulf, Gulf of Mexico, North Sea, Continental shelves of Brazil, Gulf of Guinea, etc.
Onshore
The Middle East is a dominant region for onshore oil production, with major fields located in Saudi Arabia (Khurais Complex, Ghawar Field, Shaybah, Abqaiq, Abraq Al-Tuloul, etc.), Kuwait (Greater Burgan, Wafra, etc.) and Iraq (Rumaila, Majnoon, Garraf, etc.). Ghawar Field (Saudi Arabia) is the largest conventional onshore oil field globally by reserves and output. Other regions are Russia, USA (Texas), Iran, etc.
Extraction
Offshore
Needs floating rigs, floating platforms and other subsea infrastructure that makes it capital intensive. Requires advanced technology and equipments.
Onshore
Easier drilling, cheaper infrastructure
Environmental Risks
Offshore
Drilling activities, including seismic exploration, can disturb and destroy marine habitats and ecosystems while platform discharges can reduce the abundance and diversity of benthic organisms (bottom-dwelling organisms).
Major accidents, equipment failures, or leaks in pipelines can result in significant oil releases, devastating marine and coastal ecosystems. During severe storms, tracking storms and staging evacuations from offshore platforms can be complex and hazardous.
Onshore
Drilling operations can lead to deforestation and destruction of wildlands and rangelands. Soil can be degraded by drilling fluids and waste products. Wastewater can contaminate the groundwater.
Contribution
Offshore
28% of global crude oil supply.
Onshore
72% of global crude oil supply.
Conclusion
While off-shore reserves enhance energy security and national independence, their extraction involves high costs, environmental risks like oil spills, and complex logistical challenges due to their location beneath the ocean.
