The work discusses morphology, vertical and lateral distribution, and genesis of gas-seepage marks first established in the Carboniferous coal-bearing sequence of the Lvov-Volyn Basin. The abundance of gasseepage marks inPosidonia horizons confined to the basal part of the upper coal-bearing subformation is noted. The unique character of established gas-seepage marks and the necessity of their further study for the resolution of many scientific and applied problems are emphasized.