Thermal volume expansion of Estonian kukersite kerogen was simulated with the aim to predict the response of kerogen to thermal stress in laboratory and geological conditions. The simulation was performed using a general amber force field evaluated by the calculation of non-polar cohesive energy density based on atomic interactions and value of corresponding solubility parameter. At constant pressure in the range 1-1,000 bars the specific volume vs. temperature plots were registered, and two linear regions at 150525 and 550-900 K (at the pressure one bar) we're identified. In the gap between these regions a changeover point, termed as apparent second-order polymer-like phase transition from the glassy to the rubbery state, is located. At higher pressures the changeover shifts to higher temperatures. Its possible meaning in kerogen transformations at retorting and geological conditions is discussed. A further experimental study of the observed phenomenon is needed.