A method for evaluating a degree of transformation ratio of kerogen to oil and/or gas and/or gas to oil generation index using a pyrolysis gas chromatography is disclosed. The method comprises providing (302) a rock sample in powdered form; determining (304), by a source rock analysis instrument, total organic carbon in said rock sample, remaining hydrocarbon generation potential in rock sample, and a maturity of rock sample; feeding said sample in a pyrolyzer if said sample satisfies a pre-defined condition; analyzing (306), said sample in said pyrolyzer, by heating said sample at a pre-specified pyrolysis temperature in pre-specified pyrolysis steps and for pre-specified pyrolysis time; determining (308), by a gas chromatograph, a peak area of hydrocarbons present in said sample analyzed; evaluating (310), in a said degree of transformation ratio of said sample to oil and/or gas and/or said gas to oil generation index.
