While I realize I misspoke regarding petroleum as a fuel for generating Electricity. I was referring to it's sister industry of Coal. Sorry and Thank You, for pointing that out.
While I understand the methods for generating Electricity in the Past and Present, has been driven by the Economy, I believe in the Future it will be driven by Desperation.
Observation: Throughout History mankind has been driven to develop new technologies and products because of desperation, in as much for the reason of greed.
Pump manufacturers were really keen on the Idea of using Mass Flow Meters, but, then later claimed they couldn't because of higher manufacturing costs that could not be passed on to the Stations.
(the amount of regulations regarding Gasoline Pumps were astronomical at the time.)
The Individual States still send a guy with an "old technology" prover to check customers complaints.
It's possible things have changed, but, I wouldn't bet on it.
P.S. The density of a fluid will vary from Temperature and Pressure.
Thanks,
Hammer