I noticed on the Valvoline website that they have an engine oil specifically for Compressed Natural Gas, Liquid Petroleum Gas, and Propane. There is nothing special in their PDS http://www.valvoline.com/pdf/premium_blue_geo.pdf What makes this oil different (besides marketing)?
http://www.valvoline.com/products/commercial-industrial-products/oem-endorsed-products/71
http://www.valvoline.com/products/commercial-industrial-products/oem-endorsed-products/71