Oceans and the seas occupy the area about 361 059 000 km², that makes 71 % of a surface of the Earth; they contain 1 370 323 000 km³, or 1413*10¹¹ kg of the water solution of electrolits of average concentration.

Atmospheric circulation, not everywhere equal heating of a surface, contrasts of saultiness, temperature contrasts, forces of the Moon and Sun and other phenomena cause and support active movement of water weights in World ocean. The superficial currents are most investigated and represent the system of huge circulations driven clockwise in northern hemisphere, and anticlockwise in southern hemisphere and smaller circulations with movement in opposite directions between them.

The average speed of superficial currents lays within the limits of 0,1-0,2 metres per second, though by places it reaches1 metres per second, and Golfstream is the champion - its speed is up to 3 metres per second. The charge of water in huge superficial currents makes 10⁷ - 10⁸ m³ per second, that is at least 100 times more than charge of the largest river of the world - Amazon river. The main feature of currents is that they represent a small layer on a surface of ocean, as width of currents is usually 100-1000 times more their thickness (depth).

In many cases undersuperficial currents are revealed, which flow below superficial ones in an opposite direction. The deep currents of ocean are not investigated enough. The circuit of deep circulation is constructed by specific scientifical methods and is not very reliable. Nevertheless experiments fix the current of water on the large depths.

The surface of ocean is not ideal at all, and there are "mountains" and "hollows" on it. For example, the level of water to the south from the islands of Sri-Lanka is lowered on one hundred meters, and is lifted almost on 80 at the islands of New Guinea. Northern part of Atlantic represents a plateau with the height of 67 metres, and famous Bermudas triangle is something like the boiler with the depth of 20-30 metres.

Except for such constant "relief" caused by gravitational forces, variable "relief" as waves of this or that height and length arises and collapses on a surface of ocean. Waves are basically generated by winds, but the excitement is not necessarily observed when wind blows. Waves reach the zones of calmness from those areas, where storms happen, such waves are named lop. Winds are not the only reason of occurrence of waves, Others are: changes of atmospheric pressure, eruption of underwater volcanos, earthquake etc.

World ocean is a great transport line, but it still remains dangerous and unexplored part of hydrosphere. Ship-wrecks, despite of use of the latest achievement of a science and engineering in construction of the ships, creation of satellite navigating systems, development of services of rescue by the seas, still are very often. For last 2000 years 500 ships disappear every year, so during the specified period we lost about 1 million of them. That means that we have one sunk ship for every 360 km² . Annually from 80 up to 100 tropical hurricanes happen above ocean and take 20 thousand of lifes. Small ships also disappear in the result of natural phenomena. The writer Joseph Conrad characterised ocean: " Fenerousity is alien to the ocean. Any displays of human heroism - fearlessness, courage, fidelity - that do not touch it. It stays in irresponsible consciousness of its power. It is severe, as a governor, spoiled by flattery ".