Abstract: By analyzing the cost of prospecting well in 12 main prospect areas in the three big basins in the west, the structure, influential factors, and control of the cost of marine oil and gas prospecting well are analyzed systematically. First, a basic cost model that is composed of seven types of cost (34 items) such as drilling cost, well-log cost, logging, and oil production testing cost is presented in this paper. Secondly, according to the exploration practice in the three big basins in the past few years, quantitative analysis is carried out on the effect of five major controlling factors (nine items) including geology, price, market and affiliate transaction, engineering management, and policies on the cost of prospecting well. Thirdly, a sensitivity model is applied to select the key factors that affect the cost in 12 main prospect areas. Five conclusions are made as well. For example, well test is concluded as the main factor affecting the cost of prospecting well in mid-shallow and rigid sandstone reservoir featuring in low permeability, well depth and well test are the key factors that result in the higher cost of prospecting well in deep clastic rock and volcanic rock reservoir. Finally, methods and suggestions for controlling the cost, i.e. optimize casing structure and reduce the cost of related materials such as pipes, strengthen drilling project management, reduce accident rate, and shorten drilling cycle

Key words: cost of prospecting well, cost structure, sensitivity analysis, cost control