Oxygen is an essential element for the respiration and growth of aerobic bacteria. Since actively multiplying bacteria consume oxygen at a prodigious rate and since oxygen is a sparingly‐soluble gas, aerobic bacteria are generally minutes away from consuming the total dissolved oxygen supply and are therefore always close to self destruction. Hence, understanding and measuring the rate of oxygen supply and mechanism of transport from gas to microbial cell are vital to an effectively functioning aerobic system. But over‐supply, though not having serious consequences for the bacteria, does for the operation in expenditure of needless energy. Thus the bioengineer must carefully balance oxygen supply and usage. This review examines the various aspects of oxygen transfer and utilization — beginning with the basic physical processes governing transfer of oxygen from the air into solution, followed by complication due to chemical reaction and finally the problem introduced by mass transfer coupled with chemical reaction. Oxygen solubility and its measurement are discussed. Following establishment of the fundamental parameters governing transfer, the removal process, i.e., rate of uptake of oxygen by bacteria is treated. This section is followed by a discussion of the various methods of measurement of oxygen transfer and the physical factors affecting that rate. A major section is devoted to types of aeration equipment, their description, use, efficiency, etc. The review ends with three rather short sections on oxygen transfer economics, dissolved oxygen control and utilization of pure oxygen.