The breakup rate of bubbles was studied by observing them rising in water and in glycerol solutions with mu = 1-32 mPas. A levitating technique was applied with bubbles seized in the downstream liquid flow of a diverging channel. Bubbles with volumes V-B = 0.2-0.8 c(m)3 are generally spheroid but their shape pulsates. As they wobble they have a tendency to split. The exponential decay of the number of unbroken bubbles was found, which has been characterized quantitatively by a half-life, t(1/2). The rate of breakup increased significantly with the original size of the bubble. By regression of experimental data, the proportionality t(1/2) similar to V-B(-4) has been determined. There is a significant effect of surface tension, while the effect of viscosity on the process appeared to be negligible in the bubble Reynolds number range of 60-3000 that was investigated.