Which is the largest oil field in India?

Mumbai High, formerly Bombay High is the largest oil field in India. It is an offshore oilfield located in the Arabian Sea, approximately 160km west of the Mumbai coast. It was discovered in 1974, started production in 1976. It consists of two blocks, Mumbai High North and Mumbai High South. 

Further Reading:

• NCERT Notes: Geography- Some major minerals and their characteristic
• Geography Notes