Chances are, that if you have several vehicles, of the same exact year, type, engine, transmission, etc. that have ALREADY BEEN CONVERTED to various alternative fuels, the only ones that MIGHT be less expensive to operate than the gasoline version at $4./gallon would be the CNG and electric ones.
This would include propane, ethanol, methanol, kerosene, and distillate, in addition to the previously mentioned CNG, gasoline and electric models.
And I HAVE had experience with all of the above except CNG, methanol, and electric.
This comparison does NOT include the costs of conversion.
When considering alternate fuels, consider both the cost of energy content of the fuel per BTU, AND any local or state government regulations regarding the use of that fuel. Then consider the cost of the conversion.
A better avenue (my opinion) is to make your existing vehicle more efficient.
Jon.
