The current state-of-the-art oxygen mass transfer analysis for surface aerators is essentially limited to the first-order, exponential model employed in the ASCE Standard for the Measurement of Oxygen Transfer in Clean Water. This simple model has been used for several decades to characterize the oxygen mass transfer performance of surface aerators as well as many other types of aerators. This study develops a more fundamentally rigorous oxygen mass transfer model for surface aerators which provides a more physically realistic description of the actual oxygen transfer mechanisms. This new oxygen mass transfer model separates the oxygen transfer process into a liquid spray mass transfer zone and a surface reaeration mass transfer zone. The model independently analyzes the oxygen transfer process within these two distinctively separate zones and provides the methodology and techniques for quantitatively determining the oxygen transfer rate within each of these important, but fundamentally different, oxygen mass transfer zones.