Renewable Natural Gas (RNG), also known as bio-methane or biogas, is physically identical to fossil natural gas, but is produced from non-fossil sources. Biogas is a natural product of organic decomposition in landfills, waste digesters, and agricultural waste lagoons. Because RNG comes from organic materials decomposing naturally, it is considered an environmentally friendly fuel. RNG can be transported and used identically to fossil gas on natural gas pipelines.
Because RNG is renewable, it generates data about its origin and ownership called "renewable attributes", also called RNG-A; these are the intangible green credits associated with the fact that RNG comes from a different source than natural gas. RNG-A's are similar to the green credits created by the generation of electricity from renewable sources such as solar or wind.
Think of RNG-A as representing the renewable or "green" value of the gas. Therefore these RNG-A's are sought after by businesses and utilities who wish to operate more sustainably.