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The strike by U.S. refinery workers expanded to two more plants on Sunday. Workers say they are striking because of unfair labor practices by oil companies.

Workers at BP’s Whiting, Ind., and the Husky Energy refinery in Toledo, Ohio, walked out shortly after midnight Sunday, bringing the number of plants with striking hourly workers to 11. Nine of those refineries account for 13 percent of U.S. refining capacity.

The United Steelworkers union says that U.S refinery owners led by Royal Dutch Shell have failed to discuss health and safety issues and engaged in “bad-faith bargaining, including the refusal to bargain over mandatory subjects; undue delays in providing information; impeded bargaining; and threats issued to workers if they joined the strike.”

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About 4,000 workers at refineries in California, Kentucky, Texas and Washington initially left their jobs when the strike began on Feb. 1. Another 1,440 joined the picket lines with the latest strikes.

Oil companies are continuing to operate all but one of the plants with temporary workers. BP says replacement workers will also take over operations at the Whiting and Toledo refineries.

Advanced Oil Recovery Method Being Tested

North Dakota’s Energy and Environmental Research Center will use carbon dioxide in advanced oil recovery with its first commercial well this summer.

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The center is currently in talks with partners to select a well for a demonstration site to show how much oil can be recovered using carbon dioxide. The project will start with one well, but could grow to a multipad site, officials say.

“We believe you can start much sooner,” says Tom Erickson, director of the Energy and Environmental Research Center.  He says the group would like to try it on a well drilled within the last five years.

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