FWIW, I called Amsoil bc I have 3qts of ATM 10w-30 and 1qt of 5w-30 and wanted to mix the one quart with the 10w-30 for my wife's Focus. I spoke with Jim at Amsoil's tech department. He said they don't recommend mixing however, both of the oils I wanted to mix were very similar in chemistry. He said it can cause oil consumption problems, which I found interesting. He also said don't mix S2k, S3k with the regular line as they are an entirely different animal. So, for those M1 mixaholics, be more cautious when mixing Amsoil bc each of there oils use a specified/different chemistry. This is more for the people who want to mix and extend drains btw.