Phylogeographic patterns were examined for two species of shark that are circumglobally distributed (Carcharhinus plumbeus and Carcharhinus limbatus), but restricted to coastal waters and a third species (Carcharhinus falciformis) that is circumglobally distributed, but oceanic. Analyses of mitochondrial gene sequences based on parsimony, maximum likelihood and neighbor-joining methods revealed significant genetic variation between ocean basins for all three species suggesting gene flow is restricted between ocean basins. Neither C. plumbeus nor C. limbatus populations were monophyletic. The Atlantic C. plumbeus was more closely related to a different species (C. altimus) than to con-specific members from the Pacific. The Pacific population of C. limbatus showed a similar phylogenetic pattern, being more closely related to two other species (C. tilstoni and C. amblyrhynchoides) than to the Atlantic populations of C. limbatus. Taxonomic implications are discussed in the contexts of these findings.