Abstract: The calculations of oil/gas potential of various types of organic matter are discussed in this paper. Based on material balance law of chemical reaction and organic origin of oil/gas, the total sum of oil/gas, water, carbon dioxide, and nitrogen generated from the kerogen plus the residual kerogen should be equal to that of tne initial Kerogen. The analysis in this paper illustrates that oil/gas potential calculated by material balance almost coincides with the result of experimental simulations with a variance less than 5% and it can meet the needs of geological researches and explorations of petroleum.