As the main consumer of electricity in a wastewater treatment plant, the aeration system weights most heavily on the costs of operation. Climatic changes, the 2007/08 rise in the costs of energy, and the public support for green initiatives have raised the level of awareness for our use of energy, and this has spread far beyond the circles of the environmentally concerned: energy efficiency has become one of the decisive factors in the selection of process equipment. Rightly so, because the long-term operating costs by far exceed the initial investment. There is, however no better time for impactful marketing then when the sensitivity for a relevant subject is broadly heightened. Falling in love with an appealing technology may make one blind and it behooves the engineer to accurately evaluate the characteristics of proposed aeration blowers and carefully interpret some of the claims made by various manufacturers. The most energy efficient solution must be based on actual conditions that, in reality, will vary over an extended period of time. A comparison made at one hypothetical operating point alone is merely academic and has no practical use. It is our intent to provide information that will help the engineer appropriately define the design and the evaluation criteria of various blower technologies.