But those supplies were not as limitless as they had once seemed. With demand for petroleum—both as a fuel and in its many other synthesized forms—skyrocketing, America and other Western countries turned more and more to foreign sources, chiefly in the Middle East. At the same time, oil companies continued to search for and develop new sources, including vast undersea deposits in the Gulf of Mexico and later the North Sea. Offshore drilling presented a whole new set of challenges to petroleum engineers, who responded with some truly amazing constructions, including floating platforms designed to withstand hurricane-force winds and waves. One derrick in the North Sea called "Troll" stands in 1,000 feet of water and rises 1,500 feet above the surface. It is, with the Great Wall of China, one of only two human-made structures visible from the Moon.
One way or another, the oil continued to flow. In 1900 some 150 million barrels of oil were pumped worldwide. By 2000 world production stood at 22 billion barrels—a day. But a series of crises in the 1970s, including the Arab oil embargo of 1973 and an increasing awareness of the environmental hazards posed by fossil fuels, brought more changes to the industry. Concern over an assured supply of fossil fuel encouraged prospectors, for instance, to develop new techniques for finding oil, including using the seismic waves produced artificially by literally thumping the ground to create three-dimensional images that brought hidden underground deposits into clear view and greatly reduced the fruitless drilling of so-called dry holes. Engineers developed new types of drills that not only reached deeper into the earth—some extending several miles below the surface—but could also tunnel horizontally for thousands of feet, reaching otherwise inaccessible deposits. Known reserves were squeezed as dry as they could be with innovative processes that washed oil out with injected water or chemicals and induced thermal energy. Refineries continued to find better ways to crack crude oil into more and better fuels and even developed other techniques such as reforming, which did the opposite of cracking, fashioning just-right molecules from smaller bits and pieces. And perhaps most significantly of all, natural gas—so often found with oil deposits—was finally recognized as a valuable fuel in its own right, becoming an economically significant energy source beginning in the 1960s and 1970s.