Gas turbine (GT) units (of both the industrial and the aero-derivative type) at different developmental stages are economically assessed in both simple and combined cycle. The CHP plant supplies heat (at varying levels) to an industrial plant which currently uses some existing heating device to meet this heat requirement. The following is concluded regarding the payback periods (PBPs) obtained: (i) The CHP plant efficiencies have minor impact at high electricity-to-fuel price ratios (gamma values). (ii) At lower gamma values the efficiencies, and hence the GT type selection and nature of the heat requirement, become important. New and future GTs will then offer short PBPs, compared to conventional industrial GTs. (iii) A high electrical efficiency does not regularly imply short PBPs-sometimes the situation is actually the opposite. (iv) With an advanced GT or a combined cycle the electricity production for a given heat requirement can be substantially increased, compared to that for a less advanced GT, without any substantial increase in PBP (provided that these three systems are all designed for high total efficiencies and have similar investment costs). (v) A PBP rank ordering of various CHP options is not affected by the magnitude of the gamma value. With a life-cycle cost method, CHP plants with high power-to-heat ratios (such as the most advanced simple cycle GT and combined cycles) will be put in a favourable light-particularly if the profitability requirement is low. The rank ordering of these plants also benefits from a high gamma value.