CHARLOTTE, N.C. -- Doug Steenland, CEO of Northwest Airlines ( NWA), told employees Tuesday that he and his fellow executives have a "responsibility to consider the options open to us." In a letter to employees, Steenland wrote that he would not comment on a Wall Street Journal report that Delta ( DAL) has opened merger negotiations with both Northwest and UAL's ( UAUA) United. However, he said, the airline needs to mull its options "so that we can maintain and strengthen the competitive position we have achieved." Northwest's assets include its employees, route structure, fleet, airport facilities and hubs, he said. Northwest shares gained 8.6%. Shares in UAL rose 5%, while Delta climbed 4.4%.