The purpose of this communication is to examine several assumptions concerning the drag and frictional losses in gas-lift reactors that are common to the Saez et al. (1998) and Marquez et al. (1999) models, and to some other published models. These assumptions are as follows. (1) The friction factor in the downcomer must be adjusted upward with respect to correlations for fully developed, single-phase flow in pipes in order to account for developing flow. (2) Mechanical energy losses in the gas/liquid separator and the straightening vanes can be neglected. (3) Frictional losses in the riser are adequately described by the correlation of Akita et al. (1988), which explicitly accounts for two-phase flow.