The thermal environment of sea turtle embryos has marked effects on many aspects of their development and energetics and has consequences for posthatching stages. Here we incubated Chelonia mydas embryos from Ningaloo Reef in Western Australia at a range of temperatures (27 degrees, 29 degrees, 30 degrees, 31 degrees, 32 degrees, and 30 degrees +/- 5 degrees C) to determine development rates and the pivotal temperature for sex determination. We also measured embryonic growth, oxygen consumption, and carbon dioxide production throughout development at 27 degrees and 31 degrees C. Metabolic rates were higher at 31 degrees C than at 27 degrees C, but total energy expenditure was greater at 27 degrees C, with 2,281 mL of oxygen consumed compared with 1,992 mL at 31 degrees C. Respiration at both temperatures showed a pattern typical of sea turtle embryos, with peak rates occurring at approximately 85% of development and then declining toward hatching. Hatchlings produced at higher incubation temperatures developed faster, were smaller, and had larger residual yolk masses than hatchlings produced at lower temperatures. The pivotal temperature that produced an equal sex ratio was 29.2 degrees C, with mixed sexes produced between 27.9 degrees and 30.4 degrees C. Our results showed that the Ningaloo population of C. mydas has somewhat different thermal sensitivities than other C. mydas populations and justified why is it necessary to collect population-specific data to accurately project the impacts of global warming on focal populations.