The objective of this study was to correlate the air bubble parameters in a flotation column and the surfactant concentration to the efficiency of motor oil removal from water by continuous froth flotation. C14-15(PO)(5)SO4Na (branched alcohol propoxylate sulfate, sodium salt) was used to form microemulsions with motor oil. From the microemulsion phase diagram, the minimum surfactant concentration, known as the critical microemulsion concentration (C mu C), to form a Winsor Type III microemulsion, was preliminarily selected for the froth flotation experiments. An increase in surfactant concentration was found to reduce the size and rising velocity of air bubbles in the froth flotation column, whereas the specific surface area, bubble surface area flux, bubble number flux, and residence time of the air bubbles increased with increasing surfactant concentration. The maximum removal of both motor oil and surfactant was found to correspond to the C mu C. Beyond the C mu C, the oil removal decreased with increasing the surfactant concentration because increasing the micelle concentration results in increasing oil stabilization. (C) 2009 Elsevier B.V. All rights reserved.