(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 challenge to the $53 billion deal as its final hurdle. 

The proposed merger was first announced last October, and the FTC sent a second information request to Chevron ( CVX ) two months later. Uncertainty over the deal's closing has knocked Chevron ( CVX ) shares down 1% this year compared to a 6.5% increase in energy share fund XLE .

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.