Rep. Ed Markey, D-Mass., has asked the Treasury Department to block a merger that would give royalty-free U.S. oil to China. In a letter to the department sent Monday, Markey said the merger between Chinese oil company CNOOC Ltd. and Canadian firm Nexen Inc., should be blocked \"until, at a minimum, parties to the merger agree to pay royalties to the U.S. taxpayer on all oil produced off American shores or relinquish any ownership interest in these leases.\" The Hill newspaper reported that Nexen has two oil field leases in the Gulf of Mexico that were obtained under the Deepwater Royalty Relief Act of 1995, which granted royalty waivers to companies to encourage offshore oil development. That act was made into law when the price of oil was low. Although prices have risen, an appellate court decision in 2009 said the Interior Department was stuck with the uncapped royalty waivers on any leases issued between 1996 and 2000, the newspaper said.