This guide covers identification of the key parameters that can be monitored for obtaining an indication of the condition of liquid-immersed transformers. It also covers risk/benefit analysis, sensor application, and monitoring systems application. This guide does not cover interpretation of monitoring results. The purpose of this document is to provide guidance to those who specify, apply, install and use on-line monitoring equipment on liquid-immersed power transformers and their components. Revision Standard - Active - Draft. Identification of the key parameters that can be monitored for obtaining an indication of the condition of liquid-immersed transformers is covered by this guide. It also covers risk/benefit analysis, sensor application, and monitoring systems application. This guide does not cover interpretation of monitoring results.