Which company is most responsible for getting gas into America’s tanks? Most people would guess Exxon, but it is Valero, a 27-year-old youngster in an industry dominated by centenarians.

Key facts

• Revenues: $92bn
• Net income: $5.5bn
• Employees: 22,000
• Global Fortune 500 ranking: 43

This relatively low-profile company is the US’s biggest refiner, converting more crude oil into petrol and other refined products than any other oil and gas company in the country.