In the second test, a large amount of the fluid in the fuel system leaked from a circular fitting (green plastic) on top of the fuel tank. (iihs.org)
This could be anything from a mechanical issue (low oil pressure, intake air system leak, etc.) to an electrical problem (throttle position sensor, oxygen sensors, etc.). (yourmechanic.com)
While electricity from natural gas is generally regarded as better for the climate than electricity from coal, the more the natural gas system leaks, the less climate benefit it has. (scientificamerican.com)