IEC 60567:2011 deals with the techniques for sampling free gases from gas-collecting relays from power transformers. Three methods of sampling free gases are described. The techniques described take account, on the one hand, of the problems peculiar to analyses associated with acceptance testing in the factory, where gas contents of oil are generally very low and, on the other hand, of the problems imposed by monitoring equipment in the field, where transport of samples may be by un-pressurized air freight and where considerable differences in ambient temperature may exist between the plant and the examining laboratory. Since the publication of the previous edition, CIGRE TF.D1.01.15 has made progress in several areas of dissolved gas analysis (DGA). These advances are included in this fourth edition.