RNG is essentially Methane (CH4) that has been derived from the decay of organic matter, refined, and made available for use wherever natural gas has been provided. When biomass decays it produces a number of gases including methane, carbon dioxide, oxides of nitrogen and hydrogen sulfide. This cocktail of naturally occuring material is collectively called "biogas". There are well developed processes to to segregate all the gases found in Biogas and dispose of them accordingly. For example, the Carbon Dioxide (CO2) can be use for food processing and greenhouse operations. Hydrogen Sulfide can be refine to produce Sulfur for fertilizer. And, of course, Methane can be used to replace natural gas.

However there are companies using sources such as Landfill Gas (LFG) that are a concern to many. LFG frequently contains a number of toxic gases that may not be completely removed from the RNG. Another option is to simply use LFG to create green electricity to power electric vehicles.