Mark W. Helderman Joins ONEOK Board of Directors TULSA, Okla. — Feb. 21, 2019 — The board of directors of ONEOK, Inc. (NYSE: O.) has elected Mark W. Helderman to its board, effective Feb. 19, 2019. With this election, the ONEOK board of directors now has 11 members, nine of whom are independent. “Mark is […]