I wonder why CNG[1] is not that popular in other countries. It is very cheap, it can be installed on any car (gas and even diesels) and AFAIK it produces less pollution.
"CNG may be found above oil deposits, or may be collected from landfills or wastewater treatment plants where it is known as biogas[2]."
In Argentina most gas stations have Petrol and Diesel and I'd say ~60% of them have also CNG. It is very easy to find a CNG station on cities, but harder on rural areas.