Simulation experiments of primary or oil-added source rocks(some oil was added into source rock)have been conducted.The oil expulsion efficiency and mechanism of coal at different oil saturations

temperatures

pressures

time and water saturations have been systematically studied and compared in detail with those of mudstone.The results indicate that coal-formed oil could expel its mother souree

and its expulsion efficiencies are about 5%～25%

which is 10% lower than those of mudstone at the same conditions.