The electrochemical active surface area at oxide electrodes of Pt and electrodeposited Ni, Co and Ni20Co80 alloys was evaluated in 5 M KOH solutions based on the charge for electrochemical desorption of a monolayer of overpotential deposited oxygen (OPD O) species. The in situ technique employed for the charge measurement involves galvanostatic charging (OPD O) adsorption), followed by simple discharging (OPD O desorption) experiments. It is observed that surface area estimated by this new technique for the oxidized surfaces of the metals studied here are consistent with those from a.c. impedance spectroscopy. The activity of the metal towards the oxygen evolution reaction (OER) is also discussed in terms of their active surface area estimated in this study.