US airlines just aren't worth that much. And even though it's tempting to call them a bargain, buyers aren't exactly lining up. (Why should they?) But here are the numbing numbers. The 10 largest US carriers, from American to Alaska and JeBlue, had a collective market cap of about $16.4 billion at the end of the second quarter; that's down by 61% from the end of 2007's second quarter, when they were worth just over $42 billion. People like to talk about how Southwest is worth so much, but even though it's worth more than the other nine combined at $9.4 billion, its market cap is still down from $11.2 billion a year ago.