A theoretical analysis is performed to study the catalytic reaction of CO in both high and low temperature shift converters, The study includes comparison between model predictions and data collected from local industries in Kuwait. Theoretical models are developed to simulate temperature and conversion profiles of CO in both the high and low shift converters. Good fits are obtained between the theoretical predictions of exit CO conversion and axial temperature profiles and the collected data. Calculations show the existence of an optimum feed temperature for the high temperature shift converter. Such an optimum does not exist for the low temperature shift system because of physical limitations on operating conditions.