The influence of gold loading on the electrocatalytic oxidation of glycerol over carbon supported gold nanoparticles has been investigated. Over the range of 1-20 wt% Au/C, the gold particle size distributions were similar with an overall average particle diameter of 4.6 nm and an average specific gold surface area of 43 +/- 4 m(2) g(-1). As expected, cyclic voltammetry measurements in 1 M KOH revealed that the number of electrochemically active gold sites were directly proportional to the gold loading. This observation, together with the particle size analysis, strongly suggests that the inherent electrocatalytic behaviour of the gold nanoparticles should be independent of gold loading. Despite this, very clear evidence was found to suggest that the electrocatalytic glycerol oxidation behaviour is influenced by gold loading: both the drop-off and onset potential are functions of gold loading. These findings are explained by the differences in mass transfer and subsequent accumulation of oxidation products within the electrocatalytic layers, with layers containing higher gold nanoparticle loadings having higher levels of accumulation. This increased accumulation is speculated to inhibit gold oxide formation thus shifting the characteristic drop-off in anodic current during the forward sweep of the voltammograms to higher potentials. While this accumulation allows glycerol oxidation to occur over a wider potential range, the specific activity for glycerol oxidation is reduced, presumably due to partial blocking the glycerol oxidation reaction by the adsorbed oxidation products. These findings have important implications not only for evaluating the specific activity electrocatalytic materials but also understanding the electrocatalytic oxidation of glycerol over gold nanoparticles. (C) 2014 Elsevier Ltd. All rights reserved.