Abstract: With analyses of stable carbon isotopes on various products obtained from thermal simulated experiments,the dynamical fractionating mechanisms of stable carbon isotopes of thermal evolutionary products of such as oil and its group components,gaseous hydrocarbons,and residues were studied.In add-ition a new method was proposed which could be used for distinguishing con-densates of low maturity(products of coal measures)from condensates of high maturity(products from cracking of crude oil),and for identifying the types of origin of natural gas.