I haven't had the gas checked, but we heat our house with two ventless heaters and haven't noticed any sulfur. I worked up the numbers a few years ago, and I figured that the first 12K gallons equivalent of cng would cost me around 49¢/gal. That took into consideration the $5000 cost of the FuelMaker, about 10¢/gal of electric to run it, and 10¢/gal rebuild cost for the compressor. They say that every 4K gallons, the compressor has to be rebuilt, and at the time it was $400 to get that done. I would initially buy the gas, they are charging $1.99/gal locally.