Gas concentrations in the vicinity of gas evolving electrodes obtained from application of a galvanostatic potential-transient method and from concentration overpotentiat are opposed to concentrations obtained by different and independent methods: by evaluation of bubble growth data and ofdata for the fractional gas covmge of the electrode surface. AU experimental values are taken from literature. Discussion of the concentration distribution in the boundary layer of gas evolving electrodes evidences the necessity to distinguish clearly between a supersaturation decisive in nucleation and a separate supersaturation decisive in bubble growth. NOMENCLATURE electrode area (III*) concentration decisive in bubble growth (mol/m3) concentration at the gas-liquid interface (mol/m') saturation concentration (mol/m') concentration at the solid-liquid interface (mol/m3) numerical factors (-) departure diameter (m) diffusion coefficient of gas in liquid (m'/s) current density (A/m') exponent in equation (3) molar mass of gas (kg/mol) bubble radius (m) bubble departure radius (m) time (s) residence time of the adhering bubble (6) volumetric rate of gas evolution (ma/s) number of simultaneously adhering bubbles (-) growth coefficient ( -) density of gas Q9/m3) fractional surface coverage (-) kinematic viscosity (m'/s) _ Fo' = DtR-' Fourier number of mass transport Ja' = M,p;'(c'-cS) Jakob number of mass transport 1. INTFtODUCXION