Technically speaking, there is one ocean in the world because all the ocean waters are interconnected. Nevertheless, it has been divided into 5 smaller oceans. To determine which ocean is the oldest, the age of the oldest bottom belonging to each of them was measured.
The world’s oldest ocean is the Pacific Ocean. The oldest element of this ocean floor is estimated to be around 180 million years old. However, it should be remembered that the Pacific was formed from a much older, great ancient Ocean (Panthalassa), the formation of which began about 750 million years ago.