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%.

More from Stocks

12 Stocks That Make Up the GLUM Index

12 Stocks That Make Up the GLUM Index

REPLAY: Jim Cramer on Tariff Worries, Oil, Alphabet and Centene

REPLAY: Jim Cramer on Tariff Worries, Oil, Alphabet and Centene

Worth a Stunning $6.6 Trillion, Tech Stocks Have Taken Over the Market

Worth a Stunning $6.6 Trillion, Tech Stocks Have Taken Over the Market

Video: Athens Stock Exchange CEO on What's Next for Greece's Debt Woes

Video: Athens Stock Exchange CEO on What's Next for Greece's Debt Woes

Here's Why Snap Shares Climbed Monday

Here's Why Snap Shares Climbed Monday