ISO 11158:2009 specifies the minimum requirements for new mineral oil hydraulic fluids and is intended for hydraulic systems, particularly for hydrostatic hydraulic fluid power application. The purpose of ISO 11158:2009 is for the guidance of suppliers and end users of mineral oil hydraulic fluids and for the direction of equipment manufacturers of hydraulic systems.

ISO 11158:2009 is written in a general form so that its application can accommodate various climatic conditions throughout the world. ISO 11158:2009 also stipulates the requirements for mineral-oil hydraulic fluids at the time of delivery.

Classification of fluids used in hydraulic applications is defined in ISO 6743-4. Of the categories covered by ISO 6743-4, only five types of mineral oil based fluids are embraced in ISO 11158:2009. These categories are HH, HL, HM, HV and HG.