It appears that differences in modeling the fraction of branched products in the early work can be traced to much different products being formed in the low and high temperature FTS conditions. In the present study, for low-temperature FTS, it has been shown that, while the fraction of branched products may vary with catalyst, for a given catalyst the fraction of branched products remains constant in the C-7-C-14 range. The fraction for C-4 is very similar to the one for the C-7-C-14 range for the products from eight runs, five with iron catalysts and three with cobalt catalysts. It is therefore concluded that at low-temperature FTS conditions the fraction of branched products does not vary significantly with carbon number. Essentially the same fraction of branched products are obtained using the data from the analysis of the sample as collected, after hydrogenation so that the alkenes are converted to alkanes, and after bromination to convert the alkenes to dibromides that elute from the g.c. column at much longer times than the same carbon number alkanes. Thus, it is concluded that the fraction of branching in the alkene products is the same as in the alkane products. (c) 2005 Elsevier B.V. All rights reserved.