The major cause of hydraulic failures can be traced to fluid problems, and the majority of fluid problems are contamination related. Hydraulic fluids are engineered to operate in different environmental applications and conditions. The marketplace offers a variety of hydraulic fluids - mineral oils, synthetics and water-based fluids. Product choice depends on operational environment, including pressure and temperature, as well as whether or not a fire-resistant product is needed. Cost always plays an important part in determining a product and supplier, but operational efficiencies should be the overall deciding factor in product selection.