Maximum dive depths of common diving petrels Pelecanoides urinatrix were measured monthly over > 1 year, from January 1995 to February 1996, with miniature gauges attached to the birds at Mayes Island, Kerguelen Archipelago. Overall, maximum dive depths of 347 diving petrels averaged 31 ± 6 m (range: 8–64 m), with a mode at 30–35 m. Mean maximum dive depths differed significantly over the study period. The lowest value (22 ± 8 m) was obtained in winter and it was associated with euphausiid crustaceans, suggesting a change in foraging behaviour associated with a shift in the main prey consumed. During the breeding season, birds fed mainly upon the hyperiid amphipod Themisto gaudichaudii (66% of the total number of prey), followed by the large carnivorous copepod Paraeuchaeta antarctica (15%) and zoea larvae of the crab Halicarcinus planatus (13%). Comparison of the diving capabilities of diving petrels (genus Pelecanoides) with those of other diving seabirds suggests that, relative to body mass, diving petrels can dive deeper than penguins and also possibly than alcids, and are thus the most proficient divers among birds.