Landfill odor can come from the leachate, improper landfill gas collection systems and improper utilization of daily cover in the solid waste industry. Gas samples from landfill leachate have been determined to contain ~130 Volatile Organic Compounds (VOCs) and Volatile Sulfur Compounds (VSCs) and at least 49 of them are documented as odorants. These compounds are mainly hydrocarbons, sulfur compounds, halogenalkanes, and oxygenated hydrocarbons. The process of bacteria breaking down trash in the absence of oxygen produces the common and explosive landfill gas, methane. Some of these VOCs are also very toxic. It is estimated that more than 99% of landfill gas is comprised of CH4 and CO2.