Because methane-producing bacteria (MPB) and sulfate-reducing bacteria (SRB) compete for anaerobic utilization of organic matter, the methane generation potential (Lo) decreases logarithmically with the decrease in the COD/SO4 ratio. The Lo correction coefficient equals the Lo at a particular COD/SO4 ratio divided by the maximum Lo. An Lo correction coefficient was derived each year based on the COD/SO4 ratios of waste added to the landfill. The methane generation potential was multiplied by the Lo correction coefficient in order to correct the LFG (landfill gas) generation calculation. At the second Sudokwon landfill site (2000 ~ present), the COD/SO4 ratio decreased from 11.6 in 2000 to 4.8 in 2014. Thus, the Lo correction coefficient decreased from 0.89 in 2000 to 0.42 in 2014. The LFG 2008-2014 production correction was calculated using the model equation (Scholl canyon), and was almost the same (91 ~ 113%) as the quantity measured, including LFG that was collected, flared, or allowed to diffuse through the landfill. The methane oxidation correction factor, calculated from the concentrations of nitrogen and oxygen within the landfill gas, was between 0.92 and 1 for the first landfill site and between 0.96 and 1 for the second landfill site. Air ingress into the landfill had a negligible effect on gas generation.