This paper investigates overall CO2 balances of combined heat and power (CHP) plants with CO2 capture and storage (CCS) in Kraft pulp and paper mills. The CHP plants use biomass-based fuels and feature advanced gasification and combined cycle technology. Results from simple process simulations of the considered CHP plants are presented. Based on those results and taking into account the major direct and indirect changes in CO2 emissions, the study shows that implementing CCS leads to steep emission reductions. Furthermore, a preliminary cost assessment is carried out to analyse the CO2 mitigation cost and its dependence on the distance that the CO2 must be transported to injection sites.