This paper describes the experiments designed to control bubble size during gas injection through porous media into liquid cross flow. A parametric study examined the effect of control variables on average bubble size and standard deviation. Results showed that for a given air and liquid flow rate, changing liquid channel height at the air injection site had the largest effect on bubble size and size distribution while varying porous media grade and electrolyte concentration had smaller, though significant, effects. In this study, the channel height was varied from 0.8 to 8 mm, porous media grade from 0.5 to 100 and salt concentration varied from zero to 3%. The resulting average bubble diameters were 0.085–2.5 mm.