Editor's Note: Jon D. Markman writes a weekly column for CNBC on MSN Money that is republished here on TheStreet.com. Is there anything worse than air travel these days? Combine long lines, no meals, pitiful snacks, surly attendants, cramped seats, high prices, lousy movies and overbooked flights with bad weather and a smelly, overweight seatmate, and you've got just about the worst nightmare an already stressed-out business person can ever face. And yet the airline industry -- which no one likes, and which has been the single worst investment in the stock market for decades -- has surprisingly been by far the single best performer in the stock market over the past six months. It may have quite a long way to run still. So much for the old adage about how you should invest in what you like. The easy explanation for this paradox is that crude oil prices have dropped 35% since Aug. 1. Since jet fuel is one of the largest costs for the airline industry, surely airlines' earnings strength must simply be proportionate to the decline in expenses. But easy explanations are seldom sufficient. You know that the decline in fuel costs can't be the whole story, because an index tracking major airlines -- such as AMR Corp. ( AMR), which operates American Airlines -- is up 65% since Aug. 1, or almost double the decline in oil prices. For that matter, AMR and UAL ( UAUA), which operates United Airlines, are themselves each up about 95% in the past six months -- tripling the return of more lavishly praised companies such as Google ( GOOG) and Apple ( AAPL). Something else must be at work.