This is a trick question of sorts. The correct answer can be either one, four, five or six oceans, depending on how detailed of an answer you want.
Technically, there is only one global ocean that covers 70 percent of the world in an unbroken aquatic bridge. Historically, however, humans have recognized four oceans for hundreds of years: the Arctic Ocean, Atlantic Ocean, Indian Ocean and Pacific Ocean.
Fifth ocean controversy
At the end of the 20th century, scientists began to recognize the aquatic waters surrounding Antarctica as their own ocean. In 2000, the International Hydrographic Organization defined the Southern Ocean (also known as the Antarctic Ocean) as the waters extending north from Antarctica and up to the latitude line at 60 degrees South.
Established in 1921 with headquarters in Monaco, the IHO is an international organization of 85 coastal counties that oversee international matters of aquatic interest. In 2000, when the IHO proposed that the waters around Antarctica become declared their own ocean, 28 of the 68 countries that were then members of the IHO voted. The final tally was 27-1 in favor of declaring the Antarctic waters their own official designation as an ocean (Argentina was the lone vote against). Eighteen of the countries that approved the measure agreed the waters should be officially called the Southern Ocean, though the term Antarctic Ocean is synonymous and accepted. There are still some researchers who debate about whether the Southern Ocean should be considered its own body of water or just the most southern point of the Atlantic, Indian and Pacific Oceans.
True hydrology geeks will insist there are actually six oceans in the world. The only problem is the sixth one has never been seen. In 2014, researchers from the Woods Hole Oceanographic Institute discovered evidence of a massive body of water within the earth. Though this massive body of water would be more akin to a water-filled cavern than a traditional ocean, scientists believe the body of water could have waves just like an ocean. Research also indicates that these waters located more and than 300 hundred miles into the earth may have been part of the formation of the planet approximately 4.6 billion years ago.