U.S. Gulf Coast refiners are snapping up higher volumes of Middle Eastern and South American crudes to offset the loss of Venezuelan and Mexican barrels, according to ship tracking data, a workaround solution that might be short-lived if the U.S. allows some sanctioned Venezuelan crude to return to the market. The shake-up in trade flows reflects a shortage of medium and heavy crude grades at the key Gulf Coast refining hub which has struggled in recent months to secure adequate supplies amid Mexican production and quality challenges, and Washington's pressure strategy on Venezuela's sanctioned energy industry.