Onshore oil reserves are those found on land, such as the Cambay Basin and Assam fields in India, while offshore oil reserves lie beneath the seabed, like the Mumbai High and KG-D6 basins. As onshore fields mature and deplete, offshore reserves are increasingly important for meeting global and national energy demands.

Distribution of Offshore Oil Reserves

• Middle East and Persian Gulf: Major offshore reserves in the Persian Gulf, particularly in Saudi Arabia, Iran, Iraq, Qatar, and UAE, contribute significantly to global oil production.
• North Sea: Offshore fields in the UK and Norway are among the most developed in Europe.
• Gulf of Mexico: The US and Mexico have extensive offshore drilling operations, with deep-water reserves playing a major role in energy supply.
• West Africa: Countries like Nigeria, Angola, and Ghana have large offshore reserves that are increasingly important in global oil markets.
• Brazil and South America: Brazil’s deep-water pre-salt reserves are among the largest offshore discoveries in recent decades.
• Asia-Pacific: Offshore reserves in Malaysia, Indonesia, China’s Bohai Bay, and Australia are critical regional sources.

Differences Between Offshore and Onshore Oil Reserves

Offshore oil reserves have become increasingly significant as onshore reserves mature. For example, the North Sea fields in the UK and Norway or Brazil’s pre-salt basins now account for major portions of their national output.

Advances in technology, such as ultra-deepwater drilling used in the Gulf of Mexico and automated platforms in Qatar, have enabled deeper and more efficient exploration, reshaping global energy distribution while also raising critical economic and environmental considerations.