The efficiency of aeration systems is often expressed in terms of the kilograms of oxygen dissolved per kilowatt of energy expended. If efficiencies were determined in water with a low dissolved oxygen content the results would be very good, since the lower the dissolved oxygen content of the water, the easier it is to dissolve oxygen. Conversely, as the oxygen levels approach 100% oxygen saturation, aeration efficiency approaches zero.

Other factors influencing aeration efficiency include:

Water depth
In the case of deep water tanks (over 1 metre), aeration efficiency with surface agitators is reduced as the water depth increases. However, the efficiency of bottom placed diffusers increases.

Water temperature
Efficiency of all aeration devices is reduced as water temperature increases since the solubility of oxygen is less at higher temperatures.

Water chemistry
Water chemistry has a profound influence on efficiency ratings. For example, efficiency is progressively reduced as the organic concentration of the water due to pollution, waste feed and feces increases. Conversely, as the salt or ionic concentration of the water increases, efficiencies are improved. The reason for this phenomenon is related to the affect the salt and dissolved organics have on the surface tension of the water.