NEW YORK — Crude oil prices surged to their highest levels in 19 months today as an Alaskan oil spill sparked worries over supply in an already tight market.

The benchmark U.S. crude, West Texas Intermediate for May delivery, jumped 59 cents to $20.74 a barrel in afternoon trading on the New York Mercantile Exchange futures market, its highest since August, 1987.

Alaskan North Slope crude oil rose $1 to $19.50 a barrel in the cash market where actual barrels of oil are sold.

North Sea Brent Blend crude, the most widely traded international crude, rose above $19 a barrel for the first time since October, 1987. Brent Blend for May delivery was trading at $19.35 a barrel in New York.