Well the trip is over, and I am back in Austin in summer school. The quick summary: CNG is cheaper, more fuel efficient and, lets be honest, more fun than gasoline.

I have had a chance to recheck all of my numbers and account for what was left over in the tanks. My revised estimated mpg numbers are:

Gasoline = 18.57mpg and CNG = 20.68mpg. 

Unfortunately, there were a couple of factors that prevented the CNG Tahoe – Gasoline Avalanche comparison from being perfect. I filled up with CNG 17 times on the trip, 4 of which came from unmetered dispensers. I had to guess both what I received and what the cost would have been for those fill ups.

Here are some other stats from the road:

The avg price of gasoline paid for the Avalanche was $2.64/gallon, while the average CNG price was $2.27/gallon. CNG was 14% cheaper, but when you combine that with the improved efficiency we saved 22% on fuel.

On a per mile basis, it costs 14 cents to drive a gasoline powered 2009 Avalanche one mile, but only 11 cents to drive a 2009 CNG Tahoe one mile. 

And no, the Avalanche did not weigh significantly more than the Tahoe. The OEM model has a curb weight of 5667, 402 pounds more than an OEM Tahoe. Both the Avalanche and Tahoe were converted CNG dual fuel vehicles meaning the standard conversion included the converter and engine equipment, 2 tanks and needed mounting brackets. But this special Tahoe also has 3 additional CNG tanks and the box that covered them in the back of the car, so for the sake of this extremely scientific analysis, I am going to call weight a wash.