Mississippi has become the third state to sue BP over the 2010 Gulf of Mexico oil spill. State Attorney General Jim Hood said on Friday that the state had filed suits in federal and state court. Mr. Hood said he wanted to settle, but he said BP refused to negotiate. A spokeswoman for BP did not immediately respond to a request for comment. Louisiana and Alabama sued BP earlier and are participating in a federal trial in New Orleans to determine the liability of BP and its contractors. Mississippi had not been participating because it had not sued.