LPG is Liquefied Petroleum Gas. CNG is Compressed Natural Gas. Both are good fuels for cars. I favour LPG, for two reasons. First, it often can be obtained as a rest-product of cracking crude oil, second it has a much higher energy density than CNG.
For each country, you should
- download the POI files (preferably in the OV2 format)
- download the icon bitmap file
- make sure the name portion of the files are the same
- copy those files to your device using the something like the MyPOI manager or the instructions at TomTom POI updates in TomTom forum – GPS POI.
Germany, Austria & Switzerland
Note: In Switzerland, there are relatively few LPG stations, but many CNG stations.
Download section for getting LPG and CNG stations in Germany, Switzerland and Austria: LPG & CNG Tankstellen (download).
For TomTom devices, just download the LPG or CNG files for POI and Icon:
Italy and other countries
Start your downloads at LPG Autogas in Italy – Petrol GPS POI data directory for TomTom, Garmin, Navman, SmartPhones and other GPS devices. – GPS POI Data.
Then press the Download POI File button to download the OV2 and BMP file.
–jeroen
The Wiert Corner - irregular stream of stuff 
