Kinetic models are developed for the molecular-mass distribution of the products of hydrogenolysis of mixed long-chain n-alkanes experimentally studied in the three-phase slurry reactor over nanosized cobalt-containing Fischer-Tropsch catalysts. The models are based on different hypotheses pertaining to the ratios of probabilities for the cleavage of C-C bonds as a function of their position in n-alkane chains with allowance made for the occurrence of secondary transformations of products and the vapor-liquid equilibrium in the mixture of n-alkanes in a hydrogen medium. It is demonstrated that the experimentally observed features of this distribution cannot be described in terms of the known theories of C-C bond cleavage in the hydrogenolysis of long-chain alkanes (terminal methane splitting and uniform or normal distribution of product composition). The hypothesis of a regular increase in the probability of C-C bond cleavage on going from the center of the carbon chain to its ends is advanced. Calculations performed using combinations of the distribution following this hypothesis and the normal distribution make it possible to solve the problems mentioned above.