HP Ultra is a fully synthetic 2-cycle engine oil specially suited for high performance chainsaws and power tools. This oil has outstanding engine cleaning characteristics, plus “ultra” superior lubricating qualities in comparison to other 2-cycle engine oils. It is ideal for use in STIHL 4-MIX® engines. This oil is biodegradable, degrading by 80% in 21 days. STIHL recommends a mix of 50:1 high-quality 89 octane or higher unleaded gasoline to STIHL engine oil. This same mix ratio should be used during break-in.