The sea turtle clutch of about 100 eggs is buried deeply in the nesting beach.The eggs exchange respiratory gases with the surrounding beach as their metabolic activity increases throughout the 60 day incubation. The O2 consumption of individual eggs throughout incubation is less than that of avian eggs of similar mass; however, this difference may be attributed to the difference in incubation temperature and growth rate. The O2 consumption of the sea turtle embryo is sufficiently low and the gas conductance of the shell sufficiently large that only small gas partial pressure gradients occur across the shell. However, the metabolic intensity of the entire clutch is quite large, and since gas movement through the beach is restricted, increasing gas partial pressure gradients are established between the center and periphery of the clutch and between the clutch and surrounding beach. The rate of growth and mortality of the embryos is related to respiratory gas exchange, since maximum growth and hatchling success appear to occur in respiratory environments similar to those observed in natural nests. Embryonic growth slows and mortality increases in environments in which gas exchange is reduced below naturally occurring levels. Gas exchange considerations may influence nest construction, clutch size and incubation time among sea turtles.