Texas flexes its economic muscle in many ways. With a Gross State Product of $1.3 trillion, Texas would rank as the world's 11th largest economy were it a standalone nation. Texas has lead all states in exports for nine consecutive years, nearly $207 billion in 2010 alone.

Another sign of the Texas' clout is the cluster of major companies that are based in the Lone Star State. Texas is home office for an impressive collection of companies that include world leaders in manufacturing, energy, retail, technology and aerospace and aviation.

In recent years, Texas has had the headquarters for the most Fortune 500 and Fortune 1000 companies in the country, according to Fortune magazine rankings. In 2010, three of the 10 largest publicly traded companies in the United States and 57 companies in total on the Fortune 500 list were based in Texas. Here are the top 15:

ExxonMobil
Location: Irving
2011 Revenues: $452.9 billion
What they do: International oil and gas company
Fortune 500 rank: 1
Texas rank: 1

ConocoPhillips
Location: Houston
2011 Revenues: $237.3 billion
What they do: Energy company
Fortune 500 rank: 4
Texas rank: 2

AT&T
Location: Dallas
2011 Revenues: $126.7 billion
What they do: Telecommunications services
Fortune 500 rank: 11
Texas rank: 3

Valero Energy
Location: San Antonio
2011 Revenues: $125 billion
What they do: Energy company
Fortune 500 rank: 12
Texas rank: 4

Dell
Location: Round Rock
2011 Revenues: $62 billion
What they do: Computer manufacturer
Fortune 500 rank: 44
Texas rank: 5

Enterprise Products Partners
Location: Houston
What they do: Energy company
2011 Revenues: $44.3 billion
Fortune 500 rank: 62
Texas rank: 6

Sysco
Location: Houston
What they do: Food service distributor
2011 Revenues: $39.3 billion
Fortune 500 rank: 69
Texas rank: 7

Plains All American Pipeline
Location: Houston
What they do: Oil pipeline transportation, marketing, and storage 
2011 Revenues: $34.3 billion
Fortune 500 rank: 87
Texas rank: 8

Tesoro
Location: San Antonio
What they do: Petroleum refining and marketing
2011 Revenues: $29.9 billion
Fortune 500 rank: 101
Texas rank: 9

Halliburton
Location: Houston
What they do: Energy services
2011 Revenues: $24.8 billion
Fortune 500 rank: 118 
Texas rank: 10

AMR
Location: Fort Worth
What they do: Airline
2011 Revenues: $24 billion
Fortune 500 rank: 123
Texas rank: 11

Fluor
Location: Irving
What they do: Engineering services
2011 Revenues: $23.4 billion
Fortune 500 rank: 111
Texas rank: 12

Kimberly Clark
Location: Irving
What they do: Paper-based consumer products manufacturer
2011 Revenues: $20.8 billion
Fortune 500 rank: 137
Texas rank: 13

Baker Hughes
Location: Houston
What they do: Energy services
2011 Revenues: $19.8 billion
Fortune 500 rank: 141

United Services Automobile Association
Location: San Antonio
What they do: Financial services
201` Revenues: $19 billion
Fortune 500 rank: 144
Texas rank: 15