Abstract: Thermal evolution simulation tests of kerogen of sapropel type in the immature source rocks from No. 1 Nen Section of Cretaceous of Songliao basin are carried out, together with analyses of the loss of weight due to heating and of the products of simulation tests (in gas and liquid state) to indicate the significance of heat and time of exposure to heat in the evolution of kerogen. The process of transformation of kerogen into hydrocarbons is discussed through a comparative study of the properties of its evolution products with those of oil and gas, and it is proposed that hydrocarbons are formed due to increase of temperature that leads to the constant internuclear adjustment of bonds of various functional groups of kerogen.