A method of estimating the total organic carbon content in a sample of reservoir rock from a known depth taken from a specific oil field, the sample containing a plurality of distinguishable end member components that can include oil, bitumen, soluble tar, pyrobitumen, kerogen, coal, drilling mud additives such as lubricants, mud stabilizers, lost circulation material, and other carbon-containing contaminants, the method comprising: a. determining a set of local end members for compositional modeling; b. applying compositional modeling to determine the relative proportion of each of the local end members in the sample; c. recording the values of the percent of total yield of each end member in the sample; characterized in that the method further comprises: d. obtaining values for the total hydrogen index (THI OM), the ratio of organic matter-to-pyrolizable hydrocarbons (OM/HC py), the ratio of hydrogen to carbon in the organic matter (H/C OM), the percent of Nitrogen, Oxygen, and Sulfur in the organic matter (NOS x %), and the weight of Hydrogen in the organic matter (Wt% H OM) for each EM in the sample; e. applying compositional modeling to determine the hydrocarbon yield (Yield EMx) that is attributable to each EM in the sample; f. determining the weight of organic matter, in milligrams per gram of rock, represented by the hydrocarbon yield in accordance with the following: EM x Weight OM = Yield EMx × OM / HC Pyx wherein OM/HC Py is the ratio of organic matter to pyrolizable hydrocarbons in an end member component; g. determining the weight of elemental nitrogen, sulfur and oxygen in accordance with the following: EM x Weight NSO = NSO x % × EM x Weight OM; h. determining weight of hydrogen for each end member in a sample by the equation: EM x Weight H = Wt ⁢ % H OM × EM x Weight OM; i. calculating the total organic carbon for the end member (TOC EMx) as follows: TOC EMx = EM x Weight OM − EM x Weight NSOs − EM x Weight H; and j. summing the TOC for each end member and the inert carbon present in the formation to get the reconstructed total organic carbon (TOC RCN or TOC CoMod) as follows: TOC RCN = TOC EM 1 + TOC EM 2.... TOC EMx + TOC inert. a. determining a set of local end members for compositional modeling; b. applying compositional modeling to determine the relative proportion of each of the local end members in the sample; c. recording the values of the percent of total yield of each end member in the sample; d. obtaining values for the total hydrogen index (THI OM), the ratio of organic matter-to-pyrolizable hydrocarbons (OM/HC py), the ratio of hydrogen to carbon in the organic matter (H/C OM), the percent of Nitrogen, Oxygen, and Sulfur in the organic matter (NOS x %), and the weight of Hydrogen in the organic matter (Wt% H OM) for each EM in the sample; e. applying compositional modeling to determine the hydrocarbon yield (Yield EMx) that is attributable to each EM in the sample; f. determining the weight of organic matter, in milligrams per gram of rock, represented by the hydrocarbon yield in accordance with the following: EM x Weight OM = Yield EMx × OM / HC Pyx wherein OM/HC Py is the ratio of organic matter to pyrolizable hydrocarbons in an end member component; g. determining the weight of elemental nitrogen, sulfur and oxygen in accordance with the following: EM x Weight NSO = NSO x % × EM x Weight OM; h. determining weight of hydrogen for each end member in a sample by the equation: EM x Weight H = Wt ⁢ % H OM × EM x Weight OM; i. calculating the total organic carbon for the end member (TOC EMx) as follows: TOC EMx = EM x Weight OM − EM x Weight NSOs − EM x Weight H; and j. summing the TOC for each end member and the inert carbon present in the formation to get the reconstructed total organic carbon (TOC RCN or TOC CoMod) as follows: TOC RCN = TOC EM 1 + TOC EM 2.... TOC EMx + TOC inert.