The document summarizes the different segments of the oil and gas industry value chain. It describes the upstream segment as involving exploration and production of oil and gas. The midstream segment involves transportation, storage and wholesale marketing of oil and gas. The downstream segment involves refining of oil and gas and marketing of products to consumers. It also distinguishes between integrated oil companies that operate across the value chain and independent companies focused only on exploration and production.

1. Oil and Gas Companies
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The Upstream companies searches for potential underground or
underwater crude oil and natural gas fields, drilling of exploratory
wells, and subsequently drilling and operating the wells that recover
and bring the crude oil and/or raw natural gas to the surface. The
upstream oil sector is also commonly known as the exploration and
production (E&P) sector.
The Midstream Companies involves the transportation (by pipeline,
rail, barge, or truck), storage, and wholesale marketing of crude or
refined petroleum products. The midstream operations are often
taken to include some elements of the upstream and downstream
sectors.
The Downstream Companies commonly refers to the refining of
petroleum crude oil and the processing and purifying of raw natural
gas, as well as the marketing and distribution of products derived
from crude oil and natural gas. The downstream sector touches
consumers through products such as gasoline or petrol, kerosene, jet
fuel, diesel oil, heating oil, fuel oils, lubricants, waxes, asphalt, natural
gas, and LPG as well as hundreds of petrochemicals.

2. ●
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Independent Oil and Gas Companies are non-integrated
companies which receives nearly all of its revenues from production
at the wellhead. They are exclusively in the exploration and
production segment of the industry, with no downstream marketing or
refining within their operations.
Integrated Oil & Gas Companies engages in the exploration,
production, refinement and distribution of oil and gas. Typically,
integrated companies divide their various operations into categories:
upstream, which includes all exploration and production endeavors,
and downstream, which is confined to refinement and marketing
activities.

3. Biggest Oil Companies in World
(In Order)
1. Saudi Aramco
11. Abu Dhabi National Oil Co
2. Gazprom
12. Sonatrach
3. National Iranian Oil Co.
13. Total
4. ExxonMobil
14. Petrobras
5. PetroChina
15. Rosneft
6. BP
16. Iraqi Oil Ministry
7. Royal Dutch Shell
17. Qatar Petroleum
8. Pemex
18. Lukoil
9. Chevron
19. Eni
10. Kuwait Petroleum Corp.
20. Statoil

4. Upstream Oil & Gas Companies
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Saudi Aramco (Saudi Arabia)
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NIOC (Iran)
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PDVSA (Venenzuela)
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Petrochina (China)
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Gazprom (Russia)
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Petrobras (Brazil)
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Petronas (Malaysia)
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CNPC (Asia)

5. Downstream Oil & Gas Companies
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Exxon Mobil (North America)
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PDVSA (Latin America)
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Shell (Western Europe)
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Tatneft (Eastern Europe)
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ADNOC (Middle East)
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Sinopec (Asia)
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Puma Energy (Africa)

6. Midstream Oil & Gas Companies
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Kinder Morgan Energy Partners
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Plains All American Pipeline
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Enterprise Products Partners
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Enbridge Inc.
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Spectra Energy
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Energy Transfer Partners
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Targa Resources
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Williams Partners

7. Fully Integrated Oil and Gas
Companies
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Chevron (North America)
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Petrobras (Latin America)
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Statoil (Western Europe)
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Gazprom (Eastern Europe)
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Petrixo Group (Middle East)
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PTT (Asia)
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PetroSA (Africa)

8. Independent Oil and Gas Companies
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Breitling Oil and Gas (North America)
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HRT Oil & Gas (Latin America)
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Puma Energy (Western Europe)
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Irkutsk Oil Company (Eastern Europe)
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Crescent Petroleum (Middle East)
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Phoenix Petroleum Philippines (Asia)
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Afren (Africa)

9. Top 10 Oil and Gas Companies in
India
(1) Indian Oil Corporation
(2) ONGC
(3) Bharat Petroleum
(4) Reliance Petroleum Limited
(5) Essar Oil Limited
(6) Cairn India
(7) Gas Authority of India
(8) Hindustan Petroleum Corporation
(9) Oil India Ltd
(10) Tata Petodyne

10. Other Verticals in Oil & Gas Industry
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Consultancy
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Fabrication & Construction
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Contractor Compliance
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Manufacturers & Suppliers
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Drilling & Well Services
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Other Support Services
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Engineering
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Personnel
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Environmental & Safety
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Pipeline
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Equipment Repair
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Professional Services
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Exploration & Production
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Rental
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Transportation
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Software
For Full list of Oil and Gas related Companies :
http://www.rigzone.com/search/c/companies/