top five largest7 Sep 2018 10:16
oil and gas employers in Houston
Exxon- value 218 billion
Shell - value 233 Billion
Schlumerger - Value 28 billion
Chevron - Value 110 billion
National oilwell vargo - 7.25
add to that BP, Anadarko, cocno philips and countless others.
They also have London offices- not saying they have to be close but it does help i suppose.