The major sources of energy at present are hydrocarbons (oil, gas and coal), hydroelectric power, and nuclear power. We need to seek alternate sources because of several reasons such as threat of depletion of existing resources, environmental and climatological problems (building up of carbon dioxide layers in the atmosphere, with subsequent global warming and climate change); rise in the mean sea level (inundation of many coastal areas and islands), public concerns about safety of nuclear power together with the problem of nuclear waste disposal. The major sources of energy that can be (and are) extracted from the sea at present are petroleum hydrocarbon, methane gas hydrate, wind, sea surface waves, tide, ocean thermal gradient, and water current. The major advantages of ocean energy resources include their abundance, inexhaustibility, and their non-polluting character (e.g., wind energy, wave energy, tidal energy, etc.)