Landfill gas, also referred to as biogas, is generated during the decomposition of organic solid waste in a landfill. This gas consists of about 50 percent methane (CH4), the primary component of natural gas, about 50 percent carbon dioxide (CO2), and a very small percentage of several non-methane organic compounds. These organic compounds, even at very low concentrations, can cause unpleasant odors potentially resulting in landfill complaints from neighbours of the landfill. Municipal solid waste landfills are the largest source of human-related methane emissions. At the same time, methane emissions from landfills represent a lost opportunity to capture and use a significant energy resource. Landfill gas can be used as a fuel and substitute for natural gas or other carbon based fuels.

Methane is a potent "greenhouse" gas. Its contribution to global warming is 21 times that of carbon dioxide. Landfills are responsible for almost 40% of anthropogenic methane emissions in North America. The volatile organic compounds in these gases interact with nitrous oxides to form ozone, a primary cause of smog. Methane is also potentially hazardous since it is explosive in concentrations between 5 and 15 percent by volume.

On the positive side, landfill gas is a medium-BTU energy source that can be used in engines or turbines to generate electricity or be used directly to make steam, or fuel other industrial appliances such as boilers, furnaces or evaporators. Such uses also displace the need for burning non-renewable energy resources, and can potentially delay the need for building new power plants. Other possible high BTU uses of landfill gas and biogas include the production of CNG and LNG for storage, transport or vehicle fuel.