CNOOC Ltd has agreed to buy a minority stake in four prospects in the Gulf of Mexico from Norway's Statoil, opening crude oil reserves in the U.S. Gulf to China for the first time.

CNOOC will have a 10 percent to 20 percent interest in the four exploration areas, CNOOC spokesman Xiao Zongwei told Reuters.

But the production timetable could not be confirmed, as the areas would require a relatively long exploration period, he added.

Statoil spokeswoman Mari Dotterud said CNNOC on Oct. 29 had agreed to buy a 20 percent stake in the Tucker lease, as well as 10 percent in each of the Logan, Krakatoa and Cobra leases, while Statoil remained operator in all leases.

Neither company would disclose the price tag for the deal, but analysts estimate it could be worth up to $80 million.

 (Reporting by Alison Lui in Hong Kong and Richard Solem in Oslo, editing by Will Waterman)