It was shown that molecular-mass distributions of hydrocarbons produced over Co/SiO2 · Fe(III), Co/SiO2 · Cr(III), and Co/SiO2 · Zn(II) catalysts are described well by a mathematical model proposed earlier for rationalizing the distribution of products formed in the presence of a Co/SiO2 · Zr(IV) catalyst with a probability α. This model is based on the concept that α1-hydrocarbons are produced from alkyl intermediates and α2-hydrocarbons (α1 < α2) are formed from alternative surface compounds. The primary α1-products are olefins, and ethylene is involved in chain growth with a lower value of α. Reasons for the speculation that the difference in the pattern of molecular-mass distribution of hydrocarbons produced on cobalt and iron catalysts is due to the difference in the mechanism of formation of α1-hydrocarbons are given.