Some years ago development, in the auto industry, of routine measurement of sound intensity in vector form, brought about major changes in determining sound power, particularly in improved accuracy and use in an indoor work area. However sound power is not yet being fully utilized. Accuracies within ± 10 % or ± 0.4 dB can be expected and narrow-band spectral data and intensity distributions on the integration surface can be used to identify and quantify component noise sources. In this paper new results are presented. In particular it is shown that sound power based on vector sound intensity can be determined accurately in a reverberation room.