Royal Dutch/Shell Oil Group, BP Amoco plc, Occidental Petroleum Corp. and 11 other energy and petroleum giants will jointly launch an Internet procurement marketplace. The as-yet-unnamed exchange is expected to roll out by third quarter. It will be built by vendors including Pleasanton, Calif.-based Commerce One Inc. The oil companies and vendors will jointly own the exchange, and they intend to take it public. It will allow for the purchase of everything from drilling to office supplies. Companies launching the exchange include: Royal Dutch/Shell Oil Group, London; BP Amoco plc, London; Occidental Petroleum Group, Los Angeles; Conoco Inc., Houston; The Dow Chemical Co., Midland, Mich.; Equilon Enterprises L.L.C., Houston; Mitsubishi Corp., Tokyo; Motiva Enterprises L.L.C., Houston; Phillips Petroleum Co., Bartlesville, Okla.; Repsol YPF, Madrid; Statoil, Oslo; Tosco Corp., Stamford, Conn.; Unocal, Houston; and TotalFinaElf, Paris.