The deep abiogenic synthesis of hydrocarbons is possible under the conditions of the asthenosphere. We have found that this process can also occur under the mineral and thermobaric conditions of subducting slabs. We have investigated the abiogenic synthesis of hydrocarbon systems at pressures of 2.0-6.6 GPa and temperatures of 250-600 °C. The determined lower thermobaric limit of the reaction at 280-300 °C and 2-3 GPa corresponds to a depth of 70-80 km during cold subduction. The hydrocarbon fluid formed in the slab can migrate upwards through the network of faults and fractures to form petroleum deposits.