The petrels are seabirds in the bird order Procellariiformes. They occur in three families within that group, which also includes the Albatross family, Diomedeidae. Having a fossil record that extends back at least 60 million years, it is among the older bird groupings, other than the ratites, with distant ties to penguins and loons. However, recent research shows that the Galliformes (Pheasants, Grouse and relatives), and Anseriformes (ducks, geese and swans) are older.

All the members of the order are exclusively pelagic in distribution -- returning to land only to breed.

The family Procellariidae is the main radiation of medium-sized 'true petrels', characterised by united nostrils with medium septum, and a long outer functional primary. It is dominant in the Southern Oceans, but not so in the Northern Hemisphere.

It includes a number of petrel groups

• The fulmars: 7 species: surface predators and filter feeders, breed in high latitudes but migrate along cool currents to he north. All but Fulmarus essentially confined to the south, Fulmarus apparently colonised the N hemisphere during the Tertiary.
  • The huge giant petrel s, genus Macronectes, which are convergent with the albatrosses.
  • The true fulmars, genus Fulmarus
  • Antarctic Petrel , Thalassoica antarctica
  • Cape Petrel , Daption capense
  • Snowy Petrel , Pagodroma nivea.
• The prions, genus Pachyptila. A specialised group of six very numerous species, all southern. They have a small, fulmar-like form and filter-feed on zooplankton.
• The gadfly petrels. These are large and agile short-billed petrels in the genus Pterodroma.
• Shearwaters in the genera Calonectris, Puffinus and Procellaria. The three species in the last genus are named as petrels
• Petrels of indeterminate relationships
  • Bulwer's Petrel, Bulweria bulwerii
  • Jouanin's Petrel , Bulweria fallax
  • Blue Petrel , Halobaena caerula
  • Kerguelen Petrel Lugensa brevirostris
  • Tahiti Petrel Pseudobulweria rostrata.

The family Hydrobatidae is the storm-petrels, small pelagic petrels with a fluttering flight which often follow ships.

The family Pelacanoididae is the four species of diving petrels, genus Pelacanoides. These are auk-like small petrels of the southern oceans.

The taxonomy of the petrels is complex, and several genera are intermediate.