ENERGY

Unocal Files Countersuit Against Six Oil Firms: Los Angeles-based Unocal Corp. said the counterclaim filed in U.S. District Court seeks to prohibit other oil companies from violating its patents as they gear up to produce “reformulated” gasoline under a California law that goes into effect in 1996. Chevron Corp., Exxon Corp., Mobil Corp., Shell Oil Co., Texaco Inc. and Atlantic Richfield Co. sued Unocal seeking a judgment that its patents were invalid. The oil firms say the gasoline can’t be patented because it’s not new and because it’s required by the California Air Resources Board.