This is like the tricky questions you got in high school. In a sense, there are two answers to this question, both of them right. Strictly speaking, there is only one ocean, a great body of saltwater, which altogether covers about 72% of the Earth’s surface and surrounds the planet’s great landmasses.
In more familiar terms, the one Great Ocean is divided into four principal parts, each of them known as an ocean in its own right. The Pacific Ocean covers about 18,13,00,000 square kilometers and is by far the largest ocean. It contains about 46% of the Earth’s water.
The Atlantic Ocean is the second-largest ocean, containing about 23% of the world’s water. It is much narrower and around half the size of the Pacific, covering about 8,22,17,000 square kilometers.
The Indian Ocean is the third largest ocean. Slightly smaller than the Atlantic, it covers about 7,34,26,500 square kilometers and holds 20% of the world’s water.
The Arctic Ocean, lying within the Arctic Circle and surrounding the North Pole, is the smallest ocean. This ocean spans an area of about 1,39,86,000 square kilometers, containing 4% of the world’s water. Most of the water here is frozen, as the region has extremely low temperatures in certain places. Since this ocean is the smallest one, it might not figure prominently in people’s minds when they think of very large bodies of water. Plus, the Arctic Ocean is also mostly located on the fringes of the world map. This makes it hard to locate, especially when compared to the front and center location of the Pacific Ocean.
The Great Southern or the Atlantic Ocean, which encircles Antarctica, is not officially an ocean, but an extension of the southern portions of the Pacific, Atlantic and Indian Oceans. Most countries do count the Atlantic Ocean as the fifth one, though it may not be as well-known as the Pacific or the Atlantic. For several years, though, grade-schoolers were taught that there were only four oceans on Earth. This might still be the case in some parts of the world.
The International Hydrographic Organization has determined the limited of the Southern ocean and established it as a proper ocean. The limits here include all the water that comes under 60 degrees south. Some of the water in question is frozen as well, similar to the Arctic Ocean’s.
The Atlantic Ocean is the newest ocean basin named by the authorities, so it still counts as an ocean in itself. Hence, one correct answer to the question above will be ‘five oceans’.
However, if you want to technical about it, we could say that there’s just one global ocean.
Each of the oceans above has a connection to two other oceans (at least). This might lead to the arguments that there’s actually just one ocean and the names are that of separate ocean basins. There’s also the phenomenon of thermohaline circulation (also known as the Great Ocean Conveyor or the Global Ocean Conveyor). This is a circulation that passes through all five oceans, replacing deep seawater with surface seawater and vice versa.
Then again, the right answer about the number of oceans in the world might vary according to the country you’re in. The Southern Ocean does have recognition by the U.S. Board on Geographic Names as far as the name of this body of water is concerned. The ocean boundaries have been proposed to the IHO (International Hydrographic Organization) since 2000. Still, not every country in the world agrees on the boundaries in this proposal, so IHO members still need to ratify this issue.