In the documentation, Natural gas is presented as being part of the accepted energy carrier but it is not implemented in constants.py which makes it unusable in the MVS as an energy carrier.

I deduct from the value in constants.py and this table that one should use Gas in the MVS for natural gas, this could be a usefull change in the RTD.

Note:
It would be clearer if this table has the energy carrier headline like the other tables.