AETS was contracted by the EU Delegation to support Elektromreza Srbije (EMS), Serbian Transmission System and Market Operator. In order to be in line with the current Serbian law and EU directives in the field of mineral oil management, EMS had to properly manage mineral oil (for maintenance of HV power transformers and HV circuit breakers), mineral oil waste and build mineral oil waste sumps for substations 400/X kV, 220/X kV and 110/X kV which are working without them. AETS therefore assisted EMS to:Apply the Serbian and EU environmental legislation,Organise adequate management of mineral oil and mineral oil waste.