In striking contrast to the general increase in diving ability with body mass in seabirds, amongst the Procellariiformes, the deepest dives appear to be by the smallest species. Here, we use recently developed, miniaturized time depth recorders to provide the first accurate measurement of dive depth and duration in two small Procellariiformes: Common (Pelecanoides urinatrix) and South Georgian diving petrel (P. georgicus), and compare their diving performance in relation to body mass with that of 58 seabirds from four orders. The 20 common and six South Georgia diving petrels in our study dived to considerable depths and for long periods (respective mean ± SD of 10.5 ± 4.6 and 18.1 ± 3.6 m, and 36.4 ± 9.1 and 44.2 ± 5.9 s). In relation to body mass, these dives are closely comparable to those of small alcids, which are considered to be diving specialists, and much greater than in closely related petrels. Previous work has shown that diving petrels and small alcids share a number of convergent morphological traits; our data reveal these are manifested in terms of diving ability.