well i run 10/30 or 5/30 mobil one synthetic extended performance cause i can get it for like 25 bucks for 5 quarts. anyways in my Igersoll Rand compressor if you use petrolem based oil you can run it to 65% duty cycle but with there synthetic oil you can run the compressor 100% duty cycle time. Petrolem based oils do work i think thats obvious but I think we will get to the point where synthetics will take over cause they are better oil.