Following earlier works from our laboratory, we report further experiments on oscillatory behavior in anodic oxidation of H center dot COOH and H center dot COO- anion at a low roughness Pt electrode studied by means of: (a) galvanostatic polarization; (b) linear-sweep voltammetry coupled with (c) nanogravimetry using an electrochemical quartz-crystal nanobalance (EQCN). Employment of the latter enables a complementary aspect of oscillatory processes in interfacial electrochemistry to be examined, viz. in situ mass changes at the electrode surface that can be related quantitatively to recordable passages of charge in the time-domain of each oscillation. Such measurements also provide evidence that the sharp current spikes observed at critical potentials in the cyclic voltammetry of H center dot COOH oxidation at Pt are correlated with special conditions required for onset and maintenance of oscillations. By means of the above complementary procedures of electrochemical surface science, we attempt to elucidate the changes of states of the electrode interfaces involved in the recorded electrochemical periodicity in terms of concepts of electrocatalysis and electrochemical surface science, taking into account the role of. (a) positive feedback associated with (b) an electrocatalytic step and (c) coupling between surface-reaction steps involving surface oxide formation and reductive reaction with an absorbed intermediate such as chemisorbed CO. Crown Copyright (c) 2008 Published by Elsevier B.V. All rights reserved.