With DL's very low nonfuel costs per ASM (including industry-leading low labor costs per ASM), DL can afford to buy the extra fuel for the DC-9 variants even at this year's average price of $3/gal.

When NW proudly said about 16 years ago that it would fix up its DC-9s instead of buying new fuel efficient aircraft, jetA was selling for about $0.60/gal. Fuel is now nearly five times more costly, and those MD-80s burn nearly 1,000 gal per hour.

If you really want to see the DC-9 derivatives parked in a hurry, pray that fuel prices hit $5/gal. I guarantee that DL (and AA) would promptly park each and every copy in favor of a more fuel efficient plane.