By Siobhan Hughes Of DOW JONES NEWSWIRES WASHINGTON (Dow Jones)--Sen. Barbara Mikulski (D, Md.), on Thursday said that she might subpoena Nalco Holding Co. (NLC) executives to testify at a hearing after the maker of a dispersant being used to combat a Gulf of Mexico oil spill declined to testify at a hearing. "I'm sorry they didn't come," she said at the start of a Senate Appropriations subcommittee hearing. "We're not going to subpoena them for this hearing; we might subpoena them for another hearing." BP PLC (BP, BP.LN) has been using Nalco's Corexit 9500 to break up oil that has been leaking from an undersea well. -By Siobhan Hughes, Dow Jones Newswires; (202) 862-6654; [email protected] (END) Dow Jones Newswires July 15, 2010 10:28 ET (14:28 GMT)