A drilling rig is a machine which creates holes (usually called boreholes) and/or shafts in the ground. Drilling rigs can be massive structures housing equipment used to drill water wells, oil wells, or natural gas extraction wells, or they can be small enough to be moved manually by one person. They sample sub-surface mineral deposits, test rock, soil and groundwater physical properties, and also can be used to install sub-surface fabrications, such as underground utilities, instrumentation, tunnels or wells. Drilling rigs can be mobile equipment mounted on trucks, tracks or trailers, or more permanent land or marine-based structures (such as oil platforms, commonly called 'offshore oil rigs' even if they don't contain a drilling rig). The term "rig" therefore generally refers to the complex of equipment that is used to penetrate the surface of the Earth's crust.
In 2008 alone, the United States produced an estimated 4.9 million barrels of crude oil per day and imported 9.8 million barrels per day from other countries [source: U.S. Energy Information Administration]. This oil gets refined into gasoline, kerosene, heating oil and other products. To keep up with our consumption, oil companies must constantly look for new sources of petroleum, as well as improve the production of existing wells.