Although hydrogen is not a 100% interchangeable replacement for any fossil fuel, it can be used in conjunction with fossil fuels in some cases (e.g., natural gas pipelines, gas turbine co-firing, and diesel engine injection) to reduce their carbon content. It can also be used as a feedstock to synthesize climate-neutral versions of virtually any fossil fuel limited only be the availability of carbon from biological or environmental (e.g., direct air capture) sources. It may be economically impractical to use synthesized hydrocarbons from hydrogen to produce plastics.