Overview:

The initial search for oil is carried out mostly by geologists. Many techniques are used, especially the study of landforms and seismic analysis. Where oil is thought likely test wells will be drilled. Many exploration companies are small, and are called "wildcats."

Trade Associations:

American Association of Petroleum Geologists.
January 2000 update: This URL was not working during this update.
Masera AAPG-Data Systems (GEOBYTE-DOM)
1743 East 71st St.
Tulsa, OK 74136-5108
Geological Society of America.
International Association of Drilling Contractors.
Petroleum Equipment Institute.

Yahoo Sites:

Science: Earth Sciences: Geology and Geophysics.
Business and Economy: Companies: Scientific: Geology and Geophysics.
Science: Earth Sciences: Geology and Geophysics: Exploration Geophysics.
Computers and Internet: Software: Scientific: Geology and Geophysics.

Regulation: Finding oil usually involves staking claims and drilling. Claims are regulated by the states, unless they are on federal land. Drilling is regulated under state and federal environmental laws.

Energy Information Administration (Home Page)
US Geologogical Survey provides maps, research reports and educational materials, including the National Geologic Maps Database of the USGS.

Trade periodicals and Publications:

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

Other sources:

Energy Exchange - professional association of petroleum engineers and geologists, connecting petroleum projects with financial sources.
Energy Research Clearing House is an organization be created to promote collaborative exploration and production research.

Sample oil exploration firms:

Alberta Energy Company - oil and gas exploration and production company.
Anadarko Petroleum Corporation - services for oil and gas exploration and development.
Arrowhead Minerals Corp. - junior resource company exploring for oil and gas.
Bellwether Exploration Company - independent oil and gas company engaged in the acquisition, development, exploration, and production of oil and gas properties.
Brigham Oil & Gas L.P. - oil and gas exploration and development company focusing on the implementation of 3D seismic techniques.
Cedyco Corporation - aquisition, exploration, development and production of oil and gas for the Gulf Coast Region. -- January 2000 update: This URL was not working during this update.
Cedyco Corporation (CEDYCO-DOM)
P.O. Box 27528
Houston, TX 77227
US
FX Energy - explores for oil and gas primarily in Poland and the western United States and produces oil from fields in Montana and Nevada.
Gibraltar Energy - exploration and production company, operating primarily in the Black Warrior Basin of Mississippi.
Harken Energy Corporation - explores for, develops and produces oil and gas reserves domestically and internationally.
Hilton Petroleum - exploration, development and production of onshore oil and natural gas in North America.
International Rochester Energy Corp. - Canadian based international oil and gas exploration company.
InTerraActive - specializing in prospects ignored by larger companies because of urban location.
Laser Exploration, Inc - technology that detects oil and gas deposits onshore and offshore.
Marienfeld Royalty Corporation - Buyer of minerals and royalties from income producing oil and gas properties located in the United States and Canada.
OMNI Energy Services - diversified support company that provides an integrated range of services to geophysical and exploration and production companies engaged in the acquisition of 3D on-shore seismic data.
Nu-Sky Energy, Inc. - a public oil and gas company engaged in the acquisition and development of petroleum and natural gas in Western Canada.
Petrophysics, Inc. - specializing in relating geological information from well logs to seismic data. Developing advanced synthetic seismogram technology.
PetroStar - provides a land based deep well workover service supplying rigs, extra equipment, trained crews, and living quarters.
Pinnacle Oil International Inc. - oil and gas exploration company with exclusive rights to the Stress Field Detector (SFD).
Santa Fe International Corporation - international offshore and land contract driller. Santa Fe owns and operates a fleet of 54 marine and land drilling rigs.
Techstar Exploration January 2000 update: This URL was not working during this update. (temporarily unavailable) - devoping oil and gas prospects for the industry.
Texas Meridian Resources Corporation - independent oil and natural gas exploration company.
Tidelands Geophysical Co. - seismic data gathering and petroleum exploration.
WestCastle Energy Trust - oil and gas property acquisition trust providing management on operations, development and finance. January 2000 update: This URL was not working during this update.
Westcastle Energy Trust Ltd. (WESTCASTLE-DOM)
3100 350 7th Avenue S.W.
Calgary, Alberta T2P 3N9
CA
WhitMar Exploration - maintaining an inventory of oil and gas exploration prospects for qualified investors.
Zavanna, LLC - high-tech oil and gas exploration and development company based actively exploring in 8 US and 2 Canadian basins.

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.
Arcis Corporation - seismic services for the exploration needs of the oil and gas industry.
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.
Technical Drilling Services, Inc. - author mud logging software as well as a provider of mud logging services.
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.