The energetics of 5 species of the flying fox genus Pteropus were measured with respect to ambient temperature. These data and those from 2 species in the literature were examined in relation to body size and to their distribution on continents or small islands. Log₁₀ body mass accounted for 94% of the variation in log₁₀ basal rate of metabolism of those 7 species. Females belonging to large species of Pteropus were smaller than conspecific males and consequently had lower (total) basal rates than males. No factor other than body mass in this analysis was correlated with basal rate in Pteropus. However, in the context of 21 species of pteropodids, continental Pteropus have basal rates that are 28% greater than small-island endemics. The effect of island size was not demonstrated in Pteropus, when examined alone, because the smallest species studied are small-island specialists, and the largest species live on continents, which means that effects of mass and island size are confounded, which leads to a high scaling power (1.06) for basal rate in this genus. Log₁₀ thermal conductance in Pteropus increased with log₁₀ body mass, 5 species having low thermal conductances by mammalian standards. Body temperature was independent of body mass.