Lead U.S. oil company negotiator Shell Oil Co said face-to-face negotiations on Friday with the United Steelworkers union (USW) failed to yield an agreement to end the 20-day-old U.S. refinery strike. Workers at several refineries and chemical plants were waiting for instructions to join the more than 5,000 workers at 11 plants, including nine refineries accounting for 13 percent of U.S. production capacity, walking picket lines in the largest national refinery strike since 1980. Rumors about a tentative deal between the USW and Shell Oil, which is the U.S.