Crude oil cracking to gas is the key to determining the exploration potential and strategy for deep hydrocarbon resources.Identifying the factors that affect the threshold and potential of crude oil cracking to gas as well as other possible influencing factors will provide the scientific basis for deep hydrocarbon exploration.A comparison of pyrolysis simulation experiments of crude oil,hydrous crude oil,and various water media under a constant temperature(350℃) and pressure(50 MPa) shows that water plays a large role in crude oil cracking to gas.(1) When water is added,the gas yields increase significantly,including those of alkane gases and non-hydrocarbon gases:the yield of alkane gases increases 1.8-3 times;the yields of H2 and CO2 also increase significantly.This means that water takes part in the process of crude oil cracking to gas,and supplies hydrogen.Therefore,the presence of water will dramatically enhance the potential of crude oil cracking to gas.(2) Mg2+ ions in the formation water promote the crude oil + water reaction to some extent and increase the total yield of alkane gases and the yields of both H2 and CO2 ;more interestingly,the i-C4/n-C4 and i-C5/n-C5 ratios increase significantly.This indicates that Mg2+ ions in formation water act as a catalyst,and a disproportionation reaction is involved in the crude oil + water reaction.This study helps us to understand the factors influencing crude oil cracked gas and to evaluate the hydrocarbon resources in deep sedimentary basins. Crude oil cracking to gas is the key to determining the exploration potential and strategy for deep hydrocarbon resources. Identifying the factors that affect that threshold and potential of crude oil cracking to gas as well as other possible influencing factors will provide the scientific basis for deep hydrocarbons A comparison of pyrolysis simulation experiments of crude oil, hydrous crude oil, and various water media under a constant temperature (350 ° C) and pressure (50 MPa) shows that water plays a large role in crude oil cracking to gas. When water is added, the gas yields increased significantly, including those of alkane gases and non-hydrocarbon gases: the yield of alkane gases increases 1.8-3 times; the yield of H2 and CO2 also increase significantly ..This means that water takes part in the process of crude oil cracking to gas, and supplies hydrogen.Therefore, the presence of water will dramatically enhance the potential of crude oil cracking to gas. (2) Mg2 + ions in the for mation water promote the crude oil + water reaction to some extent and increase the total yield of alkane gases and the yield of both H2 and CO2; more interestingly, the i-C4 / n-C4 and i-C5 / n-C5 ratios increase significantly.This indicates that Mg2 + ions in formation water act as a catalyst, and a disproportionation reaction is involved in the crude oil + water reaction.This study helps us to understand the factors influencing crude oil cracked gas and to evaluate the hydrocarbon resources in deep sedimentary basins.