The electrochemical generation of individual H-2 nanobubbles at Pt nanodisk electrodes immersed in a 0.5 M H2SO4 solution is reported. A sudden drop in current associated with the transport-limited reduction, of protons is observed in the i-V response at Pt nanodisk electrodes with radii of less than SO nm. This decrease in current (similar to 95% blockage) corresponds to the formation of a single H-2 nanobubble attached to the nanoelectrode that blocks proton transport to the surface. The current at which nanobubble formation occurs i(nb)(P), is independent of scan rate and H2SO4 concentration (for. [H2SO4] > 0.1 M), indicating a critical concentration profile of electrogenerated H-2 required to nucleate a nanobubble. Finite element simulation based on Fick's first law, combined with the Young Laplace equation and Henry's law, indicates that the concentration of H-2 near the nanoelectrode surface at i(nb)(p) exceeds the saturation concentration necessary to generate a nanobubble with a size comparable to the electrode size. The rapid dissolution of the nanobubble due to the high inner Laplace pressure is precisely balanced by the electrogeneration of H-2 at the partially exposed Pt surface, resulting in a dynamically stabilized nanobubble. Preliminary measurements of the i-t response during nanobubble'formation indicate a two-step nucleation and growth mechanism with time scales on the order of 100 ps (or less) and similar to 1 ms, respectively.