Hydraulic fracturing has helped boost the rate at which oil and gas can be extracted from wells, particularly in the United States. By increasing the current available supply, fracking helps to lower oil prices on a global scale. This is particularly true domestically, since oil does not have a historically strong local market in the U.S.
Basic economics states that as the supply of any good increases, its relative cost decreases. The degree to which these decreases occur depend on many factors, including the elasticity of the good. Even though oil is a natural resource, it has no productive economic use unless it is extracted. This means that the real supply, in a productive sense, is limited to what engineers and well technicians can provide. Fracking lowers the cost of oil to the extent that it allows real supply to expand.
There are limits on the extent to which fracking can be used to increase supply. Oil is scarce, and hydraulic fracturing is more expensive and complicated than traditional oil extraction. If the global supply of oil increases and oil prices drop far enough, then the high expense of fracking is no longer justified. In other words, the success of fracking eventually imposes a limit on itself, unless technological changes make the technique less costly.
In the long run, fracking could speed up the rate at which oil prices climb. When natural oil supplies approach depletion, the scarcity forces prices higher. Fracking, by increasing the rate of extraction, expedites this eventuality. It is unlikely that the world will ever completely run out of oil. Once prices climb high enough, consumers begin to look for substitutes, and it no longer becomes profitable to produce oil.