The size and shape of bubbles in an air-lift reactor were determined using direct photography and digital image analysis. Average bubble size in the reactor was mainly a function of air flow rate and vertical position in the reactor. Two methods of characterizing bubble shape were used, one based on a Fourier Series representation of the 2-D outline, and another based on the estimated surface area to volume ratio. Both methods demonstrated that non-spherical bubbles dominate in this reactor.