Tulsa-based Fortune 500 Corporations (by size):ONEOK • Williams Companies Tulsa-based Fortune 1000 Corporations (by size):Companies listed above, plus: Dollar-Thrifty Automotive Group Major Tulsa-based private corporations (Fortune's Largest Private Companies):SemGroup (5) • QuikTrip (28) • Vanguard Automotive Group (103) • Red Man Pipe and Supply (307)