The growth of a spherical gas bubble on a horizontal plane has been studied both experimentally and theoretically. Experiments with a miniature electrode have been carried out in a uniformly (super)-saturated solution of oxygen in water, with and without electrolysis. All experiments have been done at a temperature of 291 K and at (sub)atmospheric pressure(s). An analytical expression has been derived for bubble growth in a uniformly supersaturated (or superheated) liquid, which holds for all Jakob numbers. For the more complicated case of simultaneous electrolysis a power series expansion has been found suitable. The experimental results were reproducible and in all cases the agreement with theoretical models was excellent.