This research discusses the determination of the electricity tariff scheme with a certain value limit on the capacity expansion plan of the gas engine power plant (GEPP). The additional GEPP will use some of the existing GEPP resources such as land, gas supply network, electricity network, and human resources. A financial model with the incremental analysis method is designed to calculate levelized electricity rates, which is divided into 4 cost components, namely: investment costs (A), fixed operating and maintenance costs (B), fuel costs (C), and variable operating and maintenance costs. (D). Monte Carlo simulation is used to conduct a risk assessment due to the uncertainty of inflation, heat rate and availability factors. The results of the analysis shows that to achieve the electricity production target, it can be done through a combination of using other brands of machines, selecting gas suppliers, recalculating gas transportation costs, and reducing maintenance costs by performing a long-term maintenance contract (LTMC). This study considers most of the parameters that influence the determination of the tariff scheme, so that it can be used for other generator tariff scheme determination models. The result of the research on determining the tariff scheme for GEPP indicates that a tariff adjustment needs to be applied, because it has considered the uncertainty over changes in the inflation rate and the exchange rate.