Based on the geochemical characteristics of oil-cracking gas and kerogen-cracking gas revealed by simulation experiments and the chemical composition of natural gases in actual gas reservoirs,two kinds of natural gases with different relationships between C2/C3 and Cl/C2,C2/C3 and C1/C3,C2/C3 and 100×C1/(C1-C5) were identified in the Tarim Basin,and proposed further by the authors.The relationship charts of C2/C3 and C1/C2,C2/C3 and C1/C3,C2/C3 and 100×C1/(C1-C5) can be used to effectively distinguish oil-cracking gas from kerogen-cracking gas.Petroleum geological analysis of the oil-cracking gas reservoirs showed that the distribution of oil-cracking gas is mostly related with deep-seated faults or faults with a large fault throw,and the burial depth of paleo-oil reservoir is relatively high; crude oil-cracking gas resources have been evaluated by using both forward and inversion methods.The plots of C2/C3 VS.C1/C2,C2/C3 VS.C1/C3,and C2/C3 vs.100×C1/(C1-Cs) were used to distinguish between oil-cracking gas and kerogen-cracking gas,and estimate the mixed ratios of the two kinds of natural gases in the main gas reservoirs of the platform area.