The article deals with the theoretical problems of obtaining certain substrates transformation products using immobilized cells of the methane-oxidizing bacteria. This process is based on the ability of these bacteria to cometabolize the substrates which are not used for growth. The methane-oxidizing bacteria are shown to utilize ethane during growth on methanol. Cometabolism of ethane and methanol occurs due to the presence of conjugated points of these substances oxidizing reactions as well as of the oxidation products assimilation reactions. The optimal concentrations of ethane and methanol are established for the methane-oxidizing bacteria growth and for formation of the ethane oxidation products by means of the immobilized cells.