There are strict environmental regulations concerning the disposal of waste oils such as engine, gearbox or hydraulic oil. Used oils must be collected as hazardous waste, and kept well away from ground water and soil. A detailed register of all types of waste oil can be found in the German List of Wastes Ordinance (Abfallverzeichnis-Verordnung - AVV). There is also the German Waste Oil Ordinance (Altölverordnung), which sets out the exact provisions governing disposal and groups oils into four categories for collection purposes. Oils from different categories may not be mixed, and waste oils may not be combined with other types of waste.