On the basis of morphological analysis and detailed studies of lithological-facies composition and formation conditions of coal-bearing deposits the investigations of the lower part of Carboniferous deposits of the Lviv-Volyn Basin of south-western edge of the East European Platform were conducted. In particular, the available geological material was analyzed; the initial conditions of Carbonic coal-forming (Late Tournai – beginning of Late Visean) were studied and positions of the lower boundary of the coal-bearing formation were grounded; the availability of commercial coal-bearing potential (thickness of coal seams 0.6 m and more) of the lower part of Carbonic was studied; commercial coal-bearing potential of the Visean and the lower part of the Serpukhovian stages of the lower subformation of the basin was detected; the influence of intraformational and epigenetic washings and other factors that caused the formation and changes of the lower part of the coal-bearing formation, the morphology were investigated; the possibilities of commercial development of coal seams of the lower horizons were grounded. The most promising areas for searching commercial coal seams and the plots with workable thickness in deposits of the lower coal-bearing subformation were singled out for the extension of commercial coal-bearing potential and determination of the directions of searching and prospecting for promising coal deposits of the basin. It was noted that within the bounds of such areas (the Kovel area, the Bubnivska area, the Busk field and other) a continental regime was formed for a long time, and in the conditions of the marshy near-sea lowgrounds with a developed river system and dismembered paleorelief the periodical peat accumulation occurred that caused the formation of commercial coal seams. Reliable prediction of the mining-geological conditions for the development and the assessment of the commercial usability of the coal seams of the lower part of Carbonic deposits in the whole territory of the basin and within the limits of acting mines should ensure the stable development of the Lviv-Volyn Coal Basin.