Landfill gas (LFG) results from the biologic decomposition of municipal waste and consists of mostly methane (CH4) and carbon dioxide (CO2), as well as trace amounts of a variety of other compounds. In this study, the major landfill gas emissions produced in Istanbul Hasdal landfill were investigated and modeled. In the investigated area, CH4, CO2, and O-2 measurements were made for 3.5 years in order to monitor long-term variations. In addition, a supervised algorithm for the evaluation of CH4 concentration using a genetic algorithm (GA) was developed and applied to real data. The model and the actual measurement results were compared and statistically evaluated. It was observed that the long term changes of the CH4 concentrations can be estimated effectively by the GA model structure. A correlation with 0.86 value was ascertained between the actual values and model results. The results of the study indicated that the GA can be used in modeling landfill gases generated in solid waste deposition areas.