Natural gas is considered easier on the environment than other fossil fuels, since it releases less emissions into the atmosphere when burnt. Less that is than electrical power and certainly much less than coal. The latter is the reason along with water for the industrial revolution in the Ruhr region.
RWE Dea and E.ON Ruhrgas are large suppliers but residents in Rhine Ruhr often choose local public utilities. Theoretically though consumers are free to choose between many competitors on a deregulated market for their gas, which is mostly used for heating, hot water and cooking. Mostly the price of gas is artificially linked to that of electricity.
Gas stems from national sources in Germany as well as such countries as Norway and The Netherlands. New pipelines to Russia are contoversial as is the latest fracking technique to release natural gas in Germany.