Tesoro Corporation
Tesoro Corporation was a major United States petroleum refiner and marketer that operated under the Tesoro name before becoming Andeavor and being acquired by Marathon Petroleum in 2018.
Last updated October 16, 2026
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Overview
Tesoro Corporation was a San Antonio-based American petroleum refining, marketing, transportation, and distribution company. Founded in 1968 by Dr. Robert Van Osdell West Jr., the business initially concentrated on petroleum exploration and production and commissioned its first refinery near Kenai, Alaska, in 1969. Over time, it moved away from upstream exploration and built a large downstream platform focused on refining crude oil into gasoline, diesel, jet fuel, and other petroleum products, then distributing those products through wholesale channels, terminals, pipelines, maritime services, and retail stations. The company expanded especially rapidly from the late 1990s through acquisitions. It bought or acquired interests in refineries and associated assets in Hawaii, Washington, North Dakota, Utah, and California, while also adding terminals and branded retail outlets. Transactions involving the former Shell refinery at Anacortes, the Mandan and Salt Lake City refineries, the Golden Eagle refinery in Martinez, and assets purchased from BP and other oil companies transformed Tesoro from a comparatively small operator into one of the largest independent refining and marketing companies in the United States. Its refining network ultimately extended across the Western United States and included facilities in Alaska, California, Hawaii, North Dakota, Utah, and Washington. Tesoro’s retail and commercial marketing network sold fuel under several brands. In addition to its own Tesoro-branded stations, the company operated or supplied stations carrying Shell, ExxonMobil, ARCO, and USA Gasoline branding. The company also created Tesoro Logistics LP in 2011 as a master limited partnership to own and operate selected logistics infrastructure, including pipelines, terminals, and related assets. Its growth strategy combined refinery acquisitions, retail expansion, logistics integration, and efforts to concentrate on Western and inland fuel markets. In 2016, Tesoro agreed to acquire Western Refining, a transaction that expanded its geographic footprint and refining portfolio. Following that deal, the company announced a corporate name change to Andeavor, and its stock ticker changed from TSO to ANDV on August 1, 2017. The Andeavor identity was therefore a late-stage corporate brand rather than a separate long-term business unrelated to Tesoro. At the time, the company ranked among the largest independent refiners in the United States, with approximately ten refineries and reported crude-processing capacity of about 1.2 million barrels per day. Its 2017 revenue was reported at approximately $35 billion, and it ranked 90th on the 2018 Fortune 500 based on that revenue. Tesoro also faced significant environmental and safety scrutiny. Researchers identified the company as a substantial industrial air polluter, and the United States Environmental Protection Agency named it as a potentially responsible party at several Superfund sites. Tesoro settled or closed the sites in which it was involved, including one where it was characterized as a de minimis contributor. The company supported California Proposition 23, which sought to suspend implementation of the state’s climate legislation, prompting criticism from environmental groups. An explosion at the Anacortes refinery in Washington on April 2, 2010, killed seven workers and became one of the company’s most serious safety incidents. Marathon Petroleum completed its acquisition of Andeavor on October 1, 2018. The transaction ended Tesoro/Andeavor as an independent publicly traded company and combined the businesses into the largest United States refiner by capacity at that time. The Tesoro corporate brand is consequently historical and defunct as an independent company, although many acquired retail, refining, and logistics assets continued under Marathon Petroleum or other fuel brands.
History
Tesoro was established in 1968 by Robert Van Osdell West Jr. as an exploration and production company. Its transition into refining began with the opening of its first refinery near Kenai, Alaska, in 1969. The company later became the first Fortune 500 company headquartered in San Antonio, Texas, an association that helped define its corporate identity in the city. During the late 1990s and early 2000s, Tesoro redirected its business toward downstream petroleum. In 1998 it acquired a refinery in Kapolei, Hawaii, associated terminals, and approximately 30 Hawaiian retail stations from BHP Americas, while also acquiring the former Shell refinery at Anacortes, Washington. In 1999 it sold its exploration and production operations, completing its strategic shift toward refining, marketing, and logistics. In 2001, it bought refineries in Mandan, North Dakota, and Salt Lake City, Utah, from BP Amoco. The following year it acquired the Golden Eagle refinery in Martinez, California, from Ultramar, then part of Valero. Tesoro sold its marine services business to Martin Midstream in 2003 and concentrated capital on its refining and marketing platform. Its acquisitions and expansions increased refining capacity substantially, while its wholesale and retail system broadened across the Western United States. In 2005, the company undertook what it described as its largest capital expansion program to that point and reported record earnings. In 2007, it announced the purchase of Shell's Los Angeles refinery and roughly 250 Southern California retail stations, and it also acquired USA Gasoline. The company moved into a newly completed corporate campus in July 2009. In 2011, it formed Tesoro Logistics LP and acquired approximately 250 ARCO and Thrifty-style stations in Southern California. Those stations were converted to the USA Gasoline brand in 2012. In 2013, Tesoro purchased BP's Carson refinery and ARCO brand, strengthening its Southern California presence, while selling the Kapolei refinery to Par Petroleum, now known as Par Pacific Holdings. Tesoro's operating history included serious environmental and safety controversy. Air-pollution researchers ranked it among the largest corporate industrial pollution sources in the United States, citing releases of toxic chemicals including sulfuric acid. The EPA named the company as a potentially responsible party at multiple Superfund sites; the company settled or closed the sites in which it was involved. Environmental advocates also criticized its support of California Proposition 23, which would have suspended the state's Global Warming Solutions Act, and raised concerns about crude sourced from the Amazon region. The April 2010 explosion at Anacortes that killed seven workers was the company's most severe recorded workplace disaster. In 2016, Tesoro purchased Dakota Prairie Refining in Dickinson, North Dakota, and agreed to acquire Western Refining. Following completion of the Western Refining transaction, Tesoro announced that it would operate under the Andeavor name. The corporate rename and ticker change to ANDV took effect in 2017. Andeavor then entered into a definitive merger agreement with Marathon Petroleum. Marathon completed the transaction on October 1, 2018, creating the largest American refiner by capacity at the time and ending Tesoro/Andeavor's independent corporate existence.
- 2018
Acquired by Marathon Petroleum
[1]Marathon Petroleum completed its acquisition of Andeavor on October 1, 2018.
- 2017
Corporate name changes to Andeavor
[1]Following the Western Refining acquisition, Tesoro adopted the Andeavor name and changed its ticker from TSO to ANDV.
- 2016
Western Refining transaction announced
[1]Tesoro agreed to acquire Western Refining for a reported $4.1 billion.
- 2013
Carson refinery and ARCO brand acquired
[1]Tesoro purchased BP's Carson refinery and ARCO brand, while selling its Hawaii refinery.
- 2011
Tesoro Logistics LP is formed
[1]The company created a master limited partnership for selected logistics assets and expanded its Southern California retail portfolio.
- 2007
Southern California expansion
[1]Tesoro announced the purchase of Shell's Los Angeles refinery and approximately 250 Southern California retail stations, and acquired USA Gasoline.
- 2002
Golden Eagle refinery acquired
[1]Tesoro acquired the Golden Eagle refinery in Martinez, California, from Ultramar, then associated with Valero.
- 2001
Mandan and Salt Lake City refineries acquired
[1]Tesoro purchased refinery assets in North Dakota and Utah from BP Amoco.
- 1999
Exit from exploration and production
[1]Tesoro sold its exploration and production operations and focused on downstream petroleum activities.
- 1998
Major refinery acquisitions begin
[1]Tesoro acquired the Kapolei, Hawaii refinery and associated retail and terminal assets, and acquired the former Shell refinery at Anacortes, Washington.
Products and positioning
A large, vertically integrated Western United States downstream petroleum company combining refinery operations, fuel marketing, logistics infrastructure, wholesale distribution, and branded retail stations.
Petroleum products
Refined transportation fuels
Tesoro's core output included gasoline, diesel, jet fuel, and other refined petroleum products produced at its refinery network. These products were sold through wholesale, bulk, commercial, and retail channels across the Western United States.
Retail fuel
Tesoro-branded fuel stations
The Tesoro retail brand formed part of a multi-brand station network. Alongside company-operated Tesoro stations, the wider system included outlets carrying Shell, ExxonMobil, ARCO, and USA Gasoline branding.
Petroleum logistics · 2011
Tesoro Logistics LP services
Tesoro Logistics LP held and operated selected transportation, storage, terminal, and pipeline-related assets that supported the movement of crude oil and refined products between refineries, wholesale markets, and retail channels.
Controversies
2010
Anacortes refinery explosion
An explosion at Tesoro's Anacortes, Washington, refinery on April 2, 2010, killed seven workers. The incident generated significant scrutiny of refinery safety and workplace protections.
2010
Air pollution and Superfund scrutiny
Researchers identified Tesoro as a major corporate source of industrial air pollution, while the EPA named it as a potentially responsible party at several Superfund sites. The company settled or closed the sites in which it was involved.
2010
Support for California Proposition 23
Tesoro contributed more than $1 million in support of Proposition 23, an unsuccessful initiative that sought to suspend California's Global Warming Solutions Act of 2006. The contribution drew criticism from environmental organizations.
Brand decisions
2018
Merge with Marathon PetroleumM&ABackground
Andeavor remained a large independent refiner but sought a transaction that could create greater scale and operating integration.
Action taken
Marathon Petroleum acquired all outstanding Andeavor shares, completing the merger on October 1, 2018.
Aftermath
The combination formed the largest American refiner by capacity at the time and ended Tesoro/Andeavor's independent corporate existence.
2017
Rebrand as AndeavorStrategyBackground
Tesoro announced a new corporate identity after agreeing to acquire Western Refining.
Action taken
The company changed its name to Andeavor and changed its stock ticker from TSO to ANDV on August 1, 2017.
Aftermath
The Tesoro name ceased to represent the independent parent company, which subsequently merged with Marathon Petroleum.
2016
Acquire Western RefiningM&ABackground
Tesoro sought to expand its refining and marketing footprint beyond its existing Western operations.
Action taken
Tesoro agreed to purchase Western Refining in a transaction reported at $4.1 billion.
Aftermath
The acquisition led to the Andeavor corporate rebrand and increased the scale of the combined refining system.
Reported transaction value. $4.1 billion (2016 announcement)
2011
Create Tesoro Logistics LPStrategyBackground
Tesoro needed a dedicated structure for logistics infrastructure supporting its expanding refinery and marketing network.
Action taken
The company formed Tesoro Logistics LP as a master limited partnership.
Aftermath
The partnership became part of Tesoro's logistics and infrastructure operating model.
1999
Exit exploration and productionStrategyBackground
Tesoro had begun as an exploration and production company but was building a downstream refining and marketing platform.
Action taken
The company sold its exploration and production operations and concentrated on refining, marketing, transportation, and distribution.
Aftermath
The divestment enabled Tesoro to focus its later growth on refinery and fuel-marketing acquisitions.
Recent events
- 2018
Marathon Petroleum completes acquisition of Andeavor[1]
M&A
Marathon Petroleum completed its acquisition of Andeavor on October 1, ending Tesoro's existence as an independent public company.
- 2017
Tesoro adopts the Andeavor name[1]
Leadership change · Other
After the Western Refining acquisition, Tesoro announced a corporate rebranding to Andeavor and changed its stock ticker from TSO to ANDV.
- 2016
Tesoro agrees to acquire Western Refining[1]
M&A
Tesoro announced an agreement to buy Western Refining, expanding its refining and marketing presence in the Western and inland United States.
- 2011
Tesoro forms Tesoro Logistics LP[1]
Other
Tesoro established a master limited partnership to hold and operate selected logistics assets supporting its refining and marketing system.
Sources1 sources
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