The direct-current resistivity of high-density polyethylene/graphite nanosheet composites above the percolation threshold has been measured and fitted to a power law, which gives a conductivity critical exponent (0.10 +/- 0.01) and a percolation threshold (2.97 +/- 0.03). These fitted parameters are in disagreement with universal theoretical predictions, and plausible explanations of the observed discrepancies are given. The sample-to-sample fluctuations in the relative resistivity seem to obey a power law. This fluctuation behavior, if interpreted in terms of correlation-length fluctuations, yields a correlation-length critical exponent, 0.52 +/- 0.06, that is consistent with the mean-field value of 1/2. Interpretations of these experimental results imply that nonuniversal transport behavior in disordered composites is caused by composites being in a nonuniversal scaling regime. (c) 2006 Wiley Periodicals, Inc.