With a third contract offer rejected, some 24,000 U.S. refinery workers from the Gulf of Mexico to Montana prepared to head to the picket lines Saturday just hours before an existing labor agreement expires, according to AP. The nation's biggest refiner, Valero Energy Corp., said it would shut down some facilities if workers strike. So did European oil company BP PLC. Shell Oil Co., the lead negotiator for the industry, along with Exxon Mobil Corp., said its refineries would continue to make gasoline, diesel and other fuels using nonunion or replacement workers. Chemical refiners would also be affected. LyondellBassell Industries said it was bringing in managers from locations not involved in contract negotiations to keep refineries going. A strike would affect 60 producers, according to Lynne Baker, a spokeswoman for the United Steelworkers, which represents more than 30,000 oil workers in the U.S. Bobby Hollis, chairman of the negotiating committee for the Steelworkers at Valero, said it was doubtful that there would be an agreement by the midnight deadline. Thursday, union negotiators turned down the most recent offer of a 2.5 percent wage increase for each of the next three years, in addition to changes in medical coverage. The impasse comes with refiners already cutting back production and industry experts are divided over whether a strike would hit the pocketbooks of motorists. Job numbers are in free fall, which has led to unprecedented declines in miles (kilometers) driven by Americans. Antoine Halff, an analyst with Newedge Group, said workers may actually be doing the industry a favor by going on strike with demand for gasoline so low. Many of the refineries are on the Gulf Coast, near Houston and New Orleans. There are about 4,000 refinery workers in Houston alone. But the strike would reach into California, Montana, and Tennessee, which also have refineries with labor contracts expiring. Valero told employees Friday that it would close its facilities in Delaware City, Delaware, and Memphis, Tennessee, if there is a strike. The company said it would keep its Port Arthur, Texas, plant open with a contingency work force that is being trained. «We would rather reach an agreement without a work stoppage at all,» said spokesman Bill Day. Exxon Mobil said negotiations were ongoing, but that plants would remain operational until a collective bargaining agreement was reached.