A brief account of the geology of the Bombay High oilfield on the Western Shelf of India is presented. The L‐III reservoir, its development and exploration utilising a 3‐D, 3‐phase black oil mathematical model is discussed in detail.The Bombay High, a giant offshore located 160km WNW from Bombay city on the Western continental shelf of India, was discovered in 1974. It was put in production in two tears and production has been raised gradually to 240,000 b/d. There commercially exploitable hydrocarbon‐bearing zones–L‐II(limestone), S‐I (sand) and L‐III (limestone) of Miocene age have been identified. At present, the emphasis is on xploration of the L‐III reservoir which contains over 80% of the total reserves of the field. It is composed mainly of wackestone, mudstone and monor packstone. Cyclic sedimentation is identified. Each cycle is represented by four facies: in ascending order they are–lagoonal, algal mound, foraminiferal mound and coastal marsh. The porosity is mainly intergranular, intragranular, moldic, vuggy and microfissures. The solution cavities interconnected by micro‐fissures provide excellent permeability.It is a saturated reservoir with a large gas cap and extensive aquifer, which has left a narrow strip for locating production wells to give water‐or gas‐free oil production. For optimum location of production wells, a 3‐D, 3‐phase black‐oil mathematical and radial coning model was adopted. This assumes intervening shales to be non‐barrier between sub‐layers, and intervening shales within the resrvoir to be partly in communication, giving due consideration to spatial variaton in porosity and thickness of layers. This has paid dividends and reservoir performan