In addition to the marginal seas listed in the three sub-sections below, the Arctic Ocean itself is sometimes also considered a marginal sea of the Atlantic.

Terminology

• Ocean – the four to seven largest named bodies of water in the World Ocean, all of which have “Ocean” in the name.
• Sea has several definitions:
  • A marginal sea – a marginal sea is a division of an ocean, partially enclosed by islands, archipelagos, or peninsulas, adjacent to or widely open to the open ocean at the surface, and/or bounded by submarine ridges on the sea floor.
  • A division of an ocean, delineated by landforms, currents (e.g. Sargasso Sea), or specific latitude or longitude boundaries. This includes but is not limited to marginal seas, and this is the definition used for inclusion in this list.
  • The World Ocean. For example, the Law of the Sea states that all of the World Ocean is “sea”, and this is also common usage for “the sea”.
  • Any large body of water with “Sea” in the name, including lakes.
• Strait – a narrow area of water connecting two wider areas of water

There are several terms used for bulges of ocean that result from indentations of land, which overlap in definition, and which are not consistently differentiated:

• Bay – generic term; though most features with “Bay” in the name are small, some are very large
• Gulf – a very large bay, often a top-level division of an ocean or sea
• Fjord – a long bay with steep sides, typically formed by a glacier
• Bight – a bay that is typically shallower than a sound
• Sound – a large, wide bay which is typically deeper than a bight, or a strait
• Cove – a very small, typically sheltered bay

Many features could be considered to be more than one of these, and all of these terms are used in place names inconsistently; especially bays, gulfs, and bights, which can be very large or very small. This list includes large areas of water no matter the term used in the name.

Sources differ over which seas are considered marginal seas as well as which ocean a given sea is considered a marginal part of. There is no single ultimate authority on the matter.

Atlantic Ocean

The Americas

(coast-wise north to south)

• Davis Strait
• Labrador Sea
• Gulf of St. Lawrence
• Gulf of Maine
  • Bay of Fundy
  • Massachusetts Bay
  • Cape Cod Bay
• Nantucket Sound
• Vineyard Sound
• Buzzards Bay
• Narragansett Bay
• Rhode Island Sound
• Block Island Sound
• Fishers Island Sound
• Long Island Sound
  • Shelter Island Sound
  • Noyack Bay
  • Peconic Bay
  • Gardiners Bay
  • Tobaccolot Bay
  • Sag Harbor Bay
  • Three Mile Harbor
  • Long Beach Bay
  • Pipes Cove
  • Southold Bay
  • Flanders Bay
  • Napeague Bay
  • Fort Pond Bay
  • North Sea Harbor
• New York Bay
  • Upper New York Bay
  • Lower New York Bay
• Jamaica Bay
• Raritan Bay
• Sandy Hook Bay
• Delaware Bay
• Chesapeake Bay
• Albemarle Sound
• Pamlico Sound
• Gulf of Mexico
  • Florida Bay
  • Tampa Bay
  • Pensacola Bay
  • Mobile Bay
  • Vermillion Bay
  • Bay of Campeche
• Caribbean Sea
  • Gulf of Gonâve (Haiti)
  • Gulf of Honduras
  • Golfo de los Mosquitos
  • Gulf of Venezuela
    • Lake Maracaibo
  • Gulf of Paria
  • Gulf of Darién
• Argentine Sea

Europe, Africa, and Asia

• Norwegian Sea
• North Sea
  • Wadden Sea
• Baltic Sea
  • Archipelago Sea
  • Bothnian Sea
  • Central Baltic Sea
  • Gulf of Riga
  • Oresund Strait
  • Sea of Åland
• English Channel
• Irish Sea
• Celtic Sea
• Bay of Biscay
  • Cantabrian Sea
• Mediterranean Sea
  • Adriatic Sea
  • Aegean Sea
    • Argolic Gulf
    • Myrtoan Sea
    • North Euboean Gulf
    • Saronic Gulf
    • Sea of Crete
    • South Euboean Gulf
    • Icarian Sea
    • Thermaic Gulf
    • Thracian Sea
  • Alboran Sea
  • Balearic (Catalan) Sea
  • Gulf of Lion
  • Gulf of Sidra
  • Ionian Sea
    • Gulf of Corinth
  • Levantine Sea
    • Cilician Sea
  • Libyan Sea
  • Ligurian Sea
    • Gulf of Genoa
  • Sea of Sardinia
  • Sea of Sicily
    • Inland Sea, Gozo
  • Tyrrhenian Sea
• Sea of Marmara
• Black Sea
• Sea of Azov
• Gulf of Guinea

Northern islands

(east to west)

• Irminger Sea
• Denmark Strait (between Greenland and Iceland)
• Irish Sea (between Ireland and Great Britain)
• Inner Seas off the West Coast of Scotland
  • Sea of the Hebrides (Great Britain)