Mixed gases injection into a large coal sample for CO2 sequestration in coals and enhanced coalbed methane recovery was investigated using a new numerical approach. A dynamic multi-component transport ( DMCT) model was applied to simulate ternary gas (CH4-CO2-N-2) diffusion and flow behaviors for better understanding and prediction of gas injection enhanced coalbed methane (ECBM) recovery processes. Several cases were designed to analyze the effects of injection gas composition and pressure on gas displacement dynamics in a large coal sample. The calculated results suggest that mixed gas injections have similar profiles of methane recovery as pure N-2 injection, and mixtures of N-2 and CO2 reduce the ultimate methane recovery compared to pure CO2. The breakthrough time of pure CO2 injection is longer than mixed gas injections. Injection gas composition has significant effect on produced gas composition. Crown Copyright (C) 2010 Published by Elsevier Ltd. All rights reserved.