OK, my comparison, Chrysler 2.4l, 6V., 4 cyl.
(intercity travel, with some city-transit) e.g. Higuey to La Capital, etc.
Both tanks are 16 gallons
LPG: 275 miles, cost per mile: 4.82 pesos
Gasoline premium: 360 miles, cost per mile: 7.38 pesos
I had an LPG burner (hornilla) changed a year ago, from "criolla" to "italiana" for a cost of 1000 pesos and my mileage on LPG went up 40 miles.
Make sure
- change air filter at least every 12 months
- change spark plugs at least every 8 months (you should not get platinum tipped ones)* get NGK
- clean LPG converter every 6 months
My incity consumption on LPG is only 40-45% of intercity, have not measured on gasoline (for that my gasoline tank would need to get full, which it didn't get for 3 years). I don't do much incity travel in my car, I used scooter better in Higuey, faster, cheaper, easier parking, and can get in front of everybody on traffic lights, and gets me 70 miles with 200 pesos.
* NGK spark plugs are designed for LPG, as I have been reading on Internet. Some time ago I got these without even knowing they were best designed for LPG and I have seen improved performance.