Almost all developed nations have agreed to report their annual greenhouse gas (GHG) emissions, under the UN Framework Climate Change Convention of 1997. But only a few directly measure their landfill gas emissions. Most use the Intergovernmental Panel on Climate Change (IPCC) landfill gas model to calculate them. This paper examines the accuracy of these default factors, checking references cited by the IPCC for choosing each default factor. It finds that some of these studies were misquoted and several IPCC default factors have no scientific basis. The model is conservative: for example emission inventory compilers are required to avoid underestimation, rather than to find the most accurate possible estimate of emissions. Landfill gas is usually recovered with gas extraction systems, and used to generate electricity. If landfill operators’ record-keeping is not good enough, the gas is assumed to be emitted, even if methane was recovered all year. Overall, the model’s default factors appear to overstate generation of methane and landfill emissions.