As categorized by ISO 6743, there are four types of biodegradable fluids:
- Hydraulic Environmental Triglycerides (HETG)
- Hydraulic Environmental Polyalkylene Glycols (HEPG)
- Hydraulic Environmental Synthetic Esters (HEES)
- Hydraulic Environmental PAO (Polyalphaolefins) and other Synthetic Hydrocarbon Products (HEPR)