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The formation of oil and gas under the sea floor: http://www.oilnews.com.cn/bk/images/070821/A012007011.jpg China Petroleum News Center: http://www.oilnews.com.cn/bk/images/070821/A012007011.jpg How large are the reserves of oil and natural gas in the oceans? Since most of the world’s oceans have not been thoroughly explored, there is no accurate and reliable figure yet. According to statistics, the area of oil and gas reservoirs in the world’s continental shelves alone amounts to 15 million square kilometers. More than 800 such reservoirs have been discovered, along with over 1,600 oil and gas fields. The geological reserves of oil amount to 145 billion tons, while those of natural gas total 140 trillion cubic meters. Oil and gas are two organic fluid mineral resources that are closely related in terms of their origin. They are all composed of complex hydrocarbons, whose chemical components mainly include alkanes, cycloalkanes, and aromatic hydrocarbons. Through their research, scientists have confirmed that oil and natural gas are sludge formed from the remains of various ancient organisms, which, under appropriate temperature and pressure conditions, undergo a long and complex process of transformation. The formation of oil and gas requires favorable conditions for oil generation, storage space, and preservation conditions. First, there must be large water accumulation basins formed by crustal subsidence, usually shallow seas and lakes. Secondly, there must be a suitable climate to allow organisms to grow and thrive. These organisms are generally large amounts of phytoplankton, zooplankton, foraminifera, brachiopods, corals, mosses, etc., which provide abundant organic matter for the formation of oil. Third, rivers must carry large amounts of sediment into the basin, allowing generation after generation of organisms to reproduce, die, and be buried layer by layer by the sediment. When a basin is filled with sediment layers several kilometers to tens of thousands of meters thick, it becomes a complete sedimentary basin. Through crustal movements and the action of appropriate temperature and pressure, that decomposed organic matter undergoes complex changes, eventually forming oil or natural gas. Oil and gas begin to disperse in the pores of shales and sandstones. Under formation pressure, they flow and are carried to locations suitable for the fluids to remain, where they are stored. An inverted pot, with its upside-down bottom part, is the most suitable for storing oil and gas; similar geological structures are called \"oil reservoirs\". The upper part of the oil reservoir structure must be shale with very poor permeability, so that oil and gas do not escape. This layer of shale is called the “overlying layer”.