This article presents the results obtained from greenhouse gas measurements at the Belo Monte Hydropower Reservoir. The research also details how to implement the Monte Carlo method to extrapolate greenhouse gas fluxes using observed field data from the entire reservoir. The results were compared with other studies on the same hydroelectric plant and other hydropower reservoir studies in Brazil. This study found that the Belo Monte hydroelectric plant emits a range of 3.09 gCO2eq m−2 d−1 using analytical calculation or 2.06 gCO2eq m−2 d−1 using the Monte Carlo method. In terms of the energy intensity index

the emissions represent 1.79 gCO2eq kWh−1 by analytical calculation or 1.20 gCO2eq kWh−1 by Monte Carlo method simulation. The emissions are lower than those reported in previous studies

which is justifiable since emissions during the initial phase of a reservoir’s operation are more intensive. It was observed that

in this case

using the Monte Carlo method yields results close to those obtained using the analytical method

both in terms of the average value and its uncertainty. In addition

the Monte Carlo method is more sensitive to extreme values.