I had forgotten about the power loss with CNG. Checkout the
Honda Civic Gx, 20 fewer BHP and only available with automatic. I'm not up-to-date with the conversion costs for CNG but those tanks are pretty expensive. Then you have even shorter range than Ethanol and less power than Gasoline. Don't get me wrong, Natural Gas is great stuff. It's cheaper than Gasoline and we produce plenty of it domestically. But look at
this and
this comparison.
The MPG difference between Gasohol and E85 is shrinking. Regular is increasingly 84 AKI Blendstock and 10% Ethanol to make AKI 87. E85 has about 72% of the energy of Indolene which is Pure Gasoline. But E85 has 75%(74.45% TBME), E75 is 78%, and 79% of the energy per gallon of Gasohol. I'm guessing the difference is +-1% between 87 and 89 AKI, based on Premium being 3% more efficient than Regular(given an appropriate engine).