Landfill gases are formed as a result of decomposition of the organic components of the solid waste. Because of the adverse effects on both the public health and the environment, the control of landfill gas emissions requires an effective gas control system. The methods commonly applied in controlling landfill gases are combustion and/or electrical energy production. In this study, the gases in Istanbul Yakacik unsanitary landfill have been examined. Yakacik is surrounded by inhabited buildings. Since 1979, the municipal and industrial wastes of Kartal and Pendik provinces have been dumped in Yakacik landfill, which covers an area of 80000 m(2) and stores 600000 m(3) of waste. There is a landfill gas combustion plant on this rehabilitated and closed Yakacik landfill. In this study, the major landfill gases, methane (CH4), oxygen (O-2), carbon dioxide (CO2), have been investigated together with their gas flow rate and atmospheric temperatures in the year 2001. The monthly average of methane concentration obtained from Yakacik solid waste combustion plant in 2001 varies between 40 % and 67.7 % in volume and its annual average is about 51 % in volume. The total gas flow rate at the combustion plant varies between 109.5 and 228.5 m3 with an annual average of 172.5 m(3). The total amount of methane gas produced daily varies between 55.5 and 129.6 m(3) with an annual average of 87.5 m(3) depending on the gas production. Landfill gases depict an explosive behavior, when their concentration in air is between 5 % - 15 % in volume. Because of the fact that some excessive methane concentrations were measured in this combustion plant, effective combustion should continue in such cases for the sake of public health and the protection of the environment.