It was shown that molecular-mass distributions of hydrocarbons produced over Co/SiO2 center dot Fe(III), Co/SiO2 center dot Cr(III), and Co/SiO2 center dot 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 center dot Zr(IV) catalyst with a probability alpha. This model is based on the concept that alpha(1)-hydrocarbons are produced from alkyl intermediates and alpha(2)-hydrocarbons (alpha(1) < alpha(2)) are formed from alternative surface compounds. The primary alpha(1)-products are olefins, and ethylene is involved in chain growth with a lower value of alpha. 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 alpha(1)-hydrocarbons are given.