A petroleum geologist or a geophysicist, who is responsible for analyzing and interpreting the information gathered, usually heads exploration operations. Other geological specialists also may be involved in exploration activities, including paleontologists, who study fossil remains to locate oil; mineralogists, who study physical and chemical properties of mineral and rock samples; stratigraphers, who determine the rock layers most likely to contain oil and natural gas; and photogeologists, who examine and interpret aerial photographs of land surfaces. Additionally, exploration parties may include surveyors and drafters, who assist in surveying and mapping activities.

Some geologists and geophysicists work in district offices of oil companies or contract exploration firms, where they prepare and study geological maps and analyze seismic data. These scientists also may analyze samples from test drillings.

Other workers involved in exploration are geophysical prospectors. They lead crews consisting of gravity and seismic prospecting observers, who operate and maintain electronic seismic equipment; scouts, who investigate the exploration, drilling, and leasing activities of other companies to identify promising areas to explore and lease; and lease buyers, who make business arrangements to obtain the use of the land or mineral rights from their owners.
 

Petroleum engineers are responsible for planning and supervising the actual drilling operation, once a potential drillsite has been located. These engineers develop and implement the most efficient recovery method, in order to achieve maximum profitable recovery. They also plan and supervise well operation and maintenance. Drilling superintendents serve as supervisors of drilling crews, overseeing one or more drilling rigs.

Rotary drilling crews usually consist of four or five workers. Rotary drillers supervise the crew and operate machinery that controls drilling speed and pressure. Rotary-rig engine operators are in charge of engines that provide the power for drilling and hoisting. Second in charge, derrick operators work on small platforms high on rigs to help run pipe in and out of well holes and operate the pumps that circulate mud through the pipe. Rotary-driller helpers, also known as roughnecks, guide the lower ends of pipe to well openings and connect pipe joints and drill bits.

Though not necessarily part of the drilling crew, roustabouts, or general laborers, do general oilfield maintenance and construction work, such as cleaning tanks and building roads.

Pumpers and their helpers operate and maintain motors, pumps, and other surface equipment that forces oil from wells and regulate the flow, according to a schedule set up by petroleum engineers and production supervisors. In fields where oil flows under natural pressure and does not require pumping, switchers open and close valves to regulate the flow. Gaugers measure and record the flow, taking samples to check quality. Treaters test the oil for water and sediment and remove these impurities by opening a drain or using special equipment. In most fields, pumping, switching, gauging, and treating operations are automatic.

Other skilled oilfield workers include oil well cementers, who mix and pump cement into the space between the casing and well walls to prevent cave-ins; acidizers, who pump acid down the well and into the producing formation to increase oil flow; perforator operators, who use subsurface "guns" to pierce holes in the casing to make openings for oil to flow into the well bore; sample-taker operators, who take samples of soil and rock formations from wells to help geologists determine the presence of oil; and well pullers, who remove pipes, pumps, and other subsurface devices from wells for cleaning, repairing, and salvaging.

Many other skilled workers—such as welders, pipefitters, electricians, and machinists—also are employed in maintenance operations to install and repair pumps, gauges, pipes, and other equipment.

In addition to the types of workers required for onshore drilling, crews at offshore locations also need radio operators, cooks, ships' officers, sailors, and pilots. These workers make up the support personnel who work on or operate drilling platforms, crewboats, barges, and helicopters.

Most workers involved in gas processing are operators. Gas treaters tend automatically controlled treating units that remove water and other impurities from natural gas. Gas-pumping-station operators tend compressors that raise the pressure of gas for transmission in pipelines. Both types of workers can be assisted by gas-compressor operators.

Many employees in large natural gas processing plants—welders, electricians, instrument repairers, and laborers, for example—perform maintenance activities. In contrast, many small plants are automated and are checked at periodic intervals by maintenance workers or operators, or monitored by instruments that alert operators if trouble develops. In nonautomated plants, workers usually combine the skills of both operators and maintenance workers.