Sept 23 (Reuters) - The U.S. Federal Trade Commission is

expected to greenlight U.S. oil producer Chevron's ( CVX )

purchase of Hess as soon as this week, two people

familiar with the matter said, leaving Exxon Mobil's ( XOM )

challenge$53 billion deal

proposed mergersecond information request

Exxon and CNOOC Ltd, Hess's partners in a Guyana

joint venture, are challenging the deal by claiming a right of

first refusal to any sale of Hess's Guyana assets, the prize in

the proposed merger.