This paper investigates the marine reservoir effect (?R) around Palau with specific focus on environmental and oceanographic causes of variation. Two new ?R values of known-age, pre-AD 1950 Scaridae sp. fish bone from the lagoon, are compared to extant marine shell values from the western branch of the North Pacific Gyre. This review indicates thata ?Rvalueof75±6814 Cyrs for theoceanimmediatelysurrounding Palau best fits the available evidence, while a value of -52 ± 22 14C yrs should be used for the southwest lagoon. Comparison of marine and charcoal samples from archaeological deposits on Ulong Island lend support to this regional open ocean marine reservoir value, but additional analysis is required to assess the stability of this value around the archipelago and over time. The analysis highlights that careful, informed selection of radiocarbon samples is essential to produce tight radiocarbon chronologies for Pacific archaeological sites.