May 24 (Bloomberg) -- Crude oil plunged in New York because of refinery shutdowns that may increase the glut of oil at Cushing, Oklahoma, the delivery point used for benchmark futures. Prices rose in London. London-traded Brent crude, traditionally cheaper, now costs $6.54 a barrel more than New York oil, a record premium. Brent is rising on concern that supply from Nigeria or Iran may be disrupted. A government report yesterday showed the surplus of West Texas Intermediate crude stored at Cushing is growing.