Pellgunoil- i.e. petroleum lube. Keep in mind they've been selling Pellgunoil for 30+ years, long before they ever considered getting into the PCP lineup, for use on all their Co2 and pump-up guns. I would suggest that the flash point of pellgunoil (basically thin oil- i.e. SAE-5 or so) is either higher than 1500*, or that whatever the flash point, it cannot be generated in a typical pumper- i.e. no one can pump rapidly enough to approach the PCP pressure change rate that would generate the sort of heat required. That being said- one of your "uber pumpers" might (?) be a different story.