While certain freshwater turtle taxa possess a strong correlation between the δ18Ophosphate value of their bone mineral and that of their environmental water, it remains unclear whether the same correlation applies to marine turtles. Isotopic analysis of over 50 individuals representing three species (Chelonia mydas, Caretta caretta, Dermochelys coriacea) from Atlantic and Pacific waters demonstrates that the correlation is robust for the studied specimens, which include a wide range of growth stages for the loggerhead (C. caretta). In most cases, intra- and inter-bone isotopic variations are low (standard deviation < ± 0.34‰ and 0.44‰, respectively) which confirms that bone growth occurs, on average, over a narrow body temperature range (ca. ≤ ± 2.0°C) and that samples from any spot on any bone can be considered as representative of the entire skeleton. Applying the correlation between δ18Ow and δ18Obone PO4 to marine turtles may provide a new route for investigating extant marine turtle ecology and for reconstructing paleoceanic δ18Ow values.