Little is known on the food and feeding ecology of the soft-plumaged petrel Pterodroma mollis, which is the single gadfly petrel Pterodroma spp. with a circumpolar breeding distribution within the Southern Ocean. Our primary goal was to describe its diet at Kerguelen Islands, which is the southernmost breeding locality of the species. Soft-plumaged petrels fed on fish (71% by mass), and secondarily on crustaceans (22%), while cephalopods (7%) and other items (< 1%) were minor dietary components. Eight-hundred and sixty prey were identified from the pooled 33 food samples, with the 2 hyperiid amphipods Cyllopus magellanicus (48%) and Themisto gaudichaudii (35%) being the main food items by number. Owing to their larger size than crustaceans, mesopelagic fishes were the main prey by mass, with myctophids being the most important fish family in terms of both abundance (68% of the fish) and diversity (10 species). Prey distribution indicated that soft-plumaged petrels foraged primarily in oceanic subantarctic waters to feed their chicks. The oceanic life style of gadfly petrels was then highlighted by a review of their diet worldwide (20 species, 26 studies). Gadfly petrels prey mainly upon mesopelagic fishes (chiefly myctophids) and squids with their relative proportions depending on species and localities. Crustaceans are minor food items for tropical species, but they form a significant part of the food of the small- and medium-sized petrels that live in temperate and cold waters. The review underlines the need for more well-designed investigations on this globally endangered group of seabirds, since dietary information is available for only 57% of the 35 species of gadfly petrels.