Water-gas-shift (WGS) reaction plays a significant role in industrial application of Fischer Tropsch synthesis (FTS) for coal-to-liquid (CTL) processes with iron-based catalysts. This reaction provides necessary hydrogen for synthesis gas with low H-2/CO molar ratio, and has influence on concentrations of reactants, water and carbon dioxide, which in turn has effect on product distribution, rate of FTS and catalyst deactivation. We provide information on the effect of process conditions (H-2/CO feed ratio, reaction temperature and pressure), syngas conversion, and catalyst composition and activation procedure on the WGS activity. H-2/CO consumption (or usage) ratio and the exit H-2/CO ratio vary with conversion and the extent of WGS reaction. The extent of variation is much greater for H-2/CO feed ratios greater than 1.7, than it is for the CO rich syngas (H-2/CO = 0.5-1). This in turn places limits on maximum practical single pass conversion which can be achieved with different feed compositions and results in different types of operation (low single pass conversion with tail gas recycle, and high once through single pass conversion). (C) 2015 Elsevier B.V. All rights reserved.