A rigorous rate-based steady-state model of an absorber/desorber unit for the removal of CO2 by amine solutions was developed. The model, which essentially contains no empirically assigned parameters, is based on a ＇mixing cell＇ approach and considers both interphase heat and mass transfer along with simultaneous chemical reaction rates. This deterministic model, which simulates tray and packed columns at steady state, has been validated using the data of two commercial monoethanolamine (MEA) plants. For tray columns, each tray was considered to be a mixing cell, while for packed columns, the required dispersion was provided by choosing a finite number of mixing cells. For a specified CO2 slippage rate, the effects of certain operating parameters, such as type and total concentration of amine employed, flow rate and composition of entering gas, on solution circulation rate and reboiler duty can be conveniently predicted. The computer program, written in basic language, is designed in a user-friendly form and is a menu-driven interactive simulator. The mathematical model consists of non-linear algebraic equations and can be operated on a PC. A typical running time on an IBM PS/2 with 25 MHz was 4.39 s for the absorber and 1.1 s for the desorber.