Overview:

Oil occurs in certain geologic formations at varying depths in the earth's crust, and in many cases elaborate, expensive equipment is required to get it from there. The oil is usually found trapped in a layer of porous sandstone, which lies just beneath a dome-shaped or folded layer of some non-porous rock such as limestone. In other formations the oil is trapped at a fault, or break in the layers of the crust.

In the dome and folded formations natural gas is usually present just below the non-porous layer and immediately above the oil. Below the oil layer the sandstone is usually saturated with salt water. The oil is released from this formation by drilling a well and puncturing the limestone layer on either side of the limestone dome or fold. If the peak of the formation is tapped, only the gas is obtained. If the penetration is made too far from the center, only salt water is obtained. Since the formation may be several miles below the surface this is clearly a difficult business.

The oil in such formation is usually under such great pressure that it flows naturally, and sometimes with great force, from the well. However, in some cases this pressure later diminishes so that the oil must be pumped from the well. Natural gas or water is sometimes pumped into the well to replace the oil that is withdrawn. This is called "repressurizing" the oil well.

Oil wells may be either on land or under water. In North America many wells are "offshore" in the shallow parts of the oceans, especially in the Gulf of Mexico. The "crude" or unrefined oil is typically collected from individual wells by small pipelines.

Trade Associations:

American Institute of Mining, Metalurgical and Petroleum Engineers.
American Petroleum Institute.

Regulation:

Oil extraction and feeder pipelines from wells to collection tanks is regulated under state and federal environmental laws.

Energy Information Administration (home page)
--Petroleum menu page with links to many douments and databases.

Trade periodicals and other publications:

PennWell has books, maps of oil fields, directories and databases.

Other sources:

Crutchfield Energy Data - oil and gas prices for market intelligence within the petroleum and energy industry. Oil and gas prices are both current and historical to 1975.
Energy Exchange - professional association of petroleum engineers and geologists, connecting petroleum projects with financial sources.

Sample oil well engineering and geology firms:

Alliance Engineering Inc. - providing engineering and project services to support the safe and efficient development and transmission of oil and gas resources.
Applied Reservoir Engineering & Evaluation Ltd. - engineering consulting company specializing in general reservoir engineering.
ASC Consultants, Inc. - specializes in the application and development of advanced technologies for exploration and development of oil and gas worldwide
Carson Services, Inc/Aerogravity Division - acquires, processes, and interprets continuous, simultaneous airborne gravity and magnetic survey data for worldwide hydrocarbon and mineral exploration.
Cawley, Gillespie & Associates, Inc. - serves owners and operators of oil and gas properties.
Codeco Engineering Ltd - consulting oil and gas operations engineers in drilling, completions, workovers, horizontal drilling, underbalanced drilling, emergency response, oilfield construction and project management.
Collarini Engineering - petroleum reservoir engineers and geoscientists providing reserve reporting, field studies, and acqusistion and divestment work.
Creative Engineering Options, Inc. - specializes in geotechnical engineering. Projects include site evaluation, construction monitoring services, and groundwater resource development.
Dawson Geophysical - acquires and processes 3-D seismic data used in analyzing subsurface geologic conditions for the potential of oil and natural gas accumulation.
DGSI - DGSI is a petroleum geochemical laboratory offering geochemical analysis, interpretation, petroleum system studies, basin modeling, and training.
Dolphin a.s - provides the offshore industry with rig management, well services, subsea contracting, and engineering.
Egep Consultores S.A - consulting firm specializing in geology and geophysics, hydrocarbons, and management optimization.
Ensign Geophysics - specialist in seismic data processing for oil companies.
Fekete Associates Inc. - well test interpretation, economic evaluations, reservoir engineering, oil & gas gathering system optimization/deliverability studies, production engineering, suspended well reviews and geological studies.
Fugro Consulting Engineers - international engineering, geology, geotechnical, survey, data collection, DGPS, GIS, environment, software, and consulting.
Gary S. Swindell & Associates - oil and gas reserve evaluations and general reservoir engineering studies.
Geological Consulting Services - structure maps and digital data. We specialize in the Mesozoic of the entire Gulf Coast Region.
Geological Data Maps - supplies mappable correlated geological well data for petroleum industry, and provides GIS based well location maps with subsurface contour data.
Gilbert Laustsen Jung Associates Ltd - Independent geological and engineering consulting services to the petroleum industry, including rigorous economic evaluations, technical studies, advice and opinions.
Hansen Drilling Consultants - consulting services and free software.
Hydrocarbon Geoscience Consulting Ltd - Comprehensive service in specialised geoscience consultancy.
Icon Engineering Pty Ltd - offshore engineering and construction company specialising in the oil and gas industry.
J.R. Butler and Company - reservoir engineering, exploration geology, well logging and other consulting services to the gas and oil industry.
James E. Smith & Associates - offers engineering services to the oil and gas industry in East Texas and the southwestern United States.
Kary Data Consultants Ltd. - geophysical services including brokerage and management of seismic and aeromagnetic data, speculative surveys, airborne geophysical data acquisition, processing and interpretation.
Kelman Seismic Processing - seismic processing company with offices in Calgary and Houston. Find technical papers on seismic signal processing and analysis.
Lasser, Inc. - oil and gas production data.
Magnetic Pulse, Inc - Developer of technology for induction and acoustic (also cased hole) logging measurements employing pulsed power and advanced DSP. Offers technology and wireline services.
Mohajir & Associates, Inc. - specializing in petroleum engineering, geological, and geophysical studies. Serving energy and financial firms in the oil and natural gas industry.
Mustagh Resources Ltd. - geophysical consulting company providing serving the oil and gas industry worldwide.
Norward Energy Services Corp. - providing the international petroleum industry with diversified services in separation and well-flow control.
Norwegian Geotechnical Engineering - Consulting in the field of soil and rock mechanics, foundation engineering, snow avalanche research, geo-environmental engineering and reservoir mechanics.
Oilfield Audit Services, Inc. - provides full scope rig audit and BOP inspection services.
Oilfield Management, Inc. - oil business management consulting, due diligence and advice.
OPE Inc. - provides engineering and construction services to the offshore oil and gas industry.
PENCOR Group of Companies - reservoir fluid analysis (PVT), subsurface sampling, well testing equipment, mobile laboratories, early production, production enhancement.
Petro Log, Inc. - mudlogging & engineering services for the oil industry.
Petro-Marine Engineering, Inc. - specializing in engineering, procurement, and project management for the offshore oil and gas industry.
PetroDynamics, Inc. - Interpretation of oil and gas prospects or efficient production of reservoirs.
Pinnacle Oilfield Services, Inc. - drill pipe cleaning, offshore bottom hole assembly inspection, and drill collars and heavyweight inspection.
Pinnacle Technologies, Inc. - provides fracture and reservoir consulting services and diagnostic technologies.
Production Enhancement Partners (PEP), Inc. - engineers, geologists, geophysicists and other specialists engaged in maximizing recovery of proved and probable reserves from existing fields.
Profession Petroleum Services Ltd - can undertake integerated resovoir studies for single wells, groups of wells or whole fields.
Project Consulting Services, Inc. - offers services in marine construction projects, offshore platform installation and drilled pipeline crossing.
Rocky Mountain Oilfield Testing Center - field testing of petroleum and environmental technologies, tools, and processes.
Russian Petroleum Consultants Corp. - offers petroleum reservoir management, integrated reservoir studies, field operations, and software consulting services.
Sound Energy Group - geoscience and engineering consulting group dedicated to the cost-efficient discovery and production of hydrocarbon reservoirs.
Stratagraph, Inc. - providing mudlogging and geopressure detection services to the petroleum industry.
Tobosa Exploration, Inc. - oil and gas consulting including property appraisals, lease operating services, due diligence reviews and other engineering and geological services.
Tracer Technologies International - Cleveland, OH - oilfield and process tracing and radiological services company.
Welenco, Inc. - well service, video surveys, geophysical logging, well repair and perforation cleaning on water, monitoring, mining and oil wells.