I broke my generator in with standard 10w 30 oil (2 hours load on and off). I dumped it and put in synthetic 10w 30 and if I need it for an extended outage in the summer, I will use syn 10w 30 with about 1/3 of HD30 oil. After Hurricane Sandy, I ran mine for over a month so I went to 50/50 HD30, / Syn 10w30. Its still fine. I run it every year. drain the gas and run it out, then fog the cylinder. So far so good. Good luck with whatever you decide. Probably cant go wrong with the newer oils anyway.