In order to investigate the mechanism of formation of abiogenetic hydrocarbons at the depth of the Earth, experimental research on reactions between carbonates and water or water-bearing minerals was carried out at the pressure of about 1 GPa and the temperature range of 800–1500°C. The reactions took place in an open and nonequilibrium state. Chromatographic analyses of the gas products indicate that in the experiments there were generated CH4-dominated hydrocarbons, along with some CO2 and CO. Accordingly, we think there is no essential distinction between free-state water and hydroxy in the minerals in the process of hydrocarbon formation. This study indicates that reactions between carbonates and water or water-bearing minerals should be an important factor leading to the formation of abiogenetic hydrocarbons at the Earth's depth.