Oxidation studies of percolating atomic cluster films have been carried out. Bismuth clusters were deposited under high vacuum onto silicon nitride substrates between electrical contacts. Cluster films with various conductivities were exposed to air at various pressures, and the evolution of their resistance as a function of time was monitored. Exposure to air causes an increase in the film resistance, which is steeper at higher air pressures. With remarkable consistency the films' resistances after exposure to air follow a single power law as a function of time, with a power law exponent of approximately 0.16. (c) 2007 Elsevier B.V. All rights reserved.