Merger preparations between Delta Air Lines and Northwest Airlines are helped by "having people on both sides who have known each other over time," Northwest Airlines CEO Doug Steenland said Wednesday during a conference call on the airline's financial results.

Delta CEO Richard Anderson, who would be head of the merged airline, is former chief executive of Eagan, Minn.-based Northwest.

Steve Gorman, executive vice president of operations for Atlanta-based Delta, is a former Northwest executive vice president.

Northwest's chief financial officer David Davis is a former Delta finance executive.

Steenland said the companies have hit all "milestones" so far in the U.S. Justice Department's review of the proposed merger, which the companies expect to close by the end of the year pending regulatory approval.

Standard & Poor's upgraded Delta and Northwest shares Wednesday, noting the pullback in oil prices and potential benefits of the merger.

— Kelly Yamanouchi