Oil companies are no strangers to the state of Texas. Many of the largest companies in the world were founded and currently have their headquarters in Texas. Although economic recessions might lower earnings, the top-producing oil companies still regularly bring in billions of dollars per year.

ConocoPhillips

Maintaining more than 30,000 employees across the world, ConocoPhillips is the third largest energy company in the United States. It participates in a number of oil industry activities, including reservoir exploration, 3-D seismic technology and petroleum upgrading. The company resides as the seventh largest holder of reserves that are not controlled by government. The current headquarters is in Houston, Texas. The company is estimated to have assets that add up to $150 billion as of 2010.

Baker Hughes

Baker Hughes is another Houston-based company that operates all across the globe. It manufactures numerous products and services that make drilling possible. Unlike companies that perform the actual drilling on oil reserves, Baker Hughes provides equipment that focuses on lowering costs, increasing productivity and reducing risks. As of 2010, it currently has people and offices in over 90 countries.

ExxonMobil

The world's largest oil and gas company is ExxonMobil. With a history to match, Exxon stems from the original Standard Oil founder, J.D. Rockefeller. In 1911, the U.S. Supreme Court ruled that Standard Oil split into 34 different companies, one of which was Vacuum Oil, and later to become ExxonMobil. ExxonMobil performs oil and gas exploration, refining, marketing and manufacturing. As of 2010, ExxonMobil is valued at over $300 billion and is present on six continents.

Shell

Another giant, Shell has over 100,000 employees worldwide and operates in over 100 countries. As of 2010, the company accounts for roughly two percent of the world’s oil, as well as three percent of the world’s gas per year. Shell also leads oil companies in its research and development sector, regularly spending over a billion dollars. Shell stems from a transport company that was founded by Marcus Samuel in the latter half of the 19th century. Shell is headquartered in Houston, Texas and had an estimated revenue of $458.4 billion in 2008, as well as an income of $26.5 billion.