In this work, a thermochemical investigation of plasma co-gasification of municipal solid waste (MSW) and plastic solid waste (PSW) is conducted. To assess the performance of such thermochemical conversion route, specified waste mixtures were used as a feedstock in an Integrated Plasma Gasification Combined Cycle (IPGCC). The IPGCC plant model is built within Aspen Plus environment. The impact of different plasma forming gas compositions is furthermore investigated using air as the main gas and oxygen or steam as a secondary stream. Performance metrics are calculated, and it is shown that under pure air plasma gas the gasification of solo MSW resulted in higher overall performance. However, as the oxygen ratio in the plasma gas is increased, a steady improvement is observed for all waste mixtures. A plant efficiency of 38% represents the best plant performance, obtained with pure oxygen (omega = 1) as plasma gas and a feedstock consisting of 70% MSW and 30% PSW. A different trend is seen under the increase of steam ratio in the plasma forming gas as the efficiency reaches a maximum that corresponds to a specific fraction of PSW in the waste mixture. The maximum plant efficiency, in this case, is 21.7% at 34% steam ratio (sigma) in the plasma gas and at an equal fraction of MSW and PSW in the waste mixture. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.