The results of an experimental study on gas bubble formation from a submerged orifice on a cylindrical, hat or concave blade section, which is exposed to a strong liquid cross-how, are presented. The effects of the gas velocity in the orifice (3-45 m s(-1)), the liquid cross-flow velocity (0.5-4 m s(-1)) and the blade configuration on the mode of bubble formation and the detached bubble size are investigated using high-speed flash photography. The results show that when the orifice is positioned in, or close to, an unseparated how region the predominant bubbling mode is jetting. In contrast, when the orifice is positioned within-the wake region behind the blade, the bubbles are generated individually at the orifice. For a fixed gas velocity, the detached bubble size decreases significantly with increasing liquid velocity, by approximately 50 %, between 1 and 3 m s(-1); at liquid velocities greater than 3 m s(-1), the bubble size decreases more slowly. For a fixed liquid velocity, the bubble size increases approximately linearly with increasing gas velocity through the orifice.