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The gecko Oedura marmorata was studied in two different climatic zones: the arid zone of central Australia and ill the wet-dry tropics of northern Australia. Doubly labelled water was used to measure field metabolic rate (FMR) and water Aux rates of animals in the field during the temperate seasons of spring, summer and winter, and during the tropical wet and dry seasons. FMRs were highest in the tropical wet season and lowest in the temperate winter. The geckos in central Australia expended less energy than predicted for a similarly sized iguanid lizard, but geckos from the tropics expended about the same amount of energy as predicted for an iguanid. Water flux rates of geckos from the arid zone were extremely low in all seasons compared to other reptiles, and although water flux was higher in tropical geckos, the rates were low compared to other tropical reptiles, The standard metabolic rates (SMRs) of geckos were similar between the two regions and among the seasons. Geckos selected higher body temperatures (T(b)s) in a laboratory thermal gradient in the summer (33.5 degrees C) and wet (33.8 degrees C)seasons compared to the winter (31.7 degrees C) and dry (31.4 degrees C) seasons. The mean Tbs Selected in the laboratory thermal gradient by geckos from the two regions were not different at a given time of year, The energy expended during each season was partitioned into components of resting metabolism, Tb and activity. Most of the energy expended by geckos from central Australia could be attributed to the effects of temperature on resting lizards in all three seasons. bur the energy expended by tropical geckos includes a substantial component due to activity during both seasons. This study revealed variability in patterns of ecological energetics between populations of closely related geckos, differences which cannot be entirely attributed to seasonal or temperature effects.