The evolution of oxygen gas bubbles in potassium hydroxide solution is observed in situ under microgravity by a charge-coupled device camera, focusing on the wettability of a platinum electrode modified by thiol self-assembled monolayers. Single bubble measurements on the microwire electrode reveal a three-step growth process involving (1) the nucleation and formation of a supersaturated layer of dissolved gas followed by (2) a rapid growth phase depending on the gas diffusion process, and finally, (3) a stable growth phase where the growth rate is dominated by the bubble configuration depending on the contact angle. Moreover, correlation of multiple gas bubble observations with electrochemical data and surface coverage on the plate electrode reinforce the important role of wettability in determining bubble motion and energy consumption during electrolysis under microgravity. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.