This is big news. Kayak.com appears to be referring fare searchers to fare results on Southwest Airlines' along with those of other airlines. It's not exactly a side by side comparison: you have to click a link to see what Southwest is offering on the route you searched (assuming that Southwest flies the route, of course). We first learned of this from David Landsel's New York Post travel blog. The only thing is, Southwest hates this sort of thing. They simply do not want their fares compared with those of other airlines. Just ask Sidestep.com, when they tried it a few years ago. As far as we can make out, Kayak did not reach some sort of detente with Southwest. They're just doing it to see what Southwest's reaction might be. In the past, that reaction has taken the form of a strongly worded cease and desist order. Take a look at their site's terms of use and you'll see that they clearly that that Southwest's "company information" cannot be used for commercial purposes except with permission.

We quote: "You may not use any "deep-link," "page-scrape," "robot," "spider" or other automatic device, program, algorithm or methodology which does the same things, to access, acquire, copy, or monitor any portion of the Southwest web sites or any Company Information."

Perhaps Kayak is hoping that Southwest will look the other way, since technically this is not a side by side comparison.

This should be interesting. If nothing else, it will get Kayak some media attention.

Note: Airfarewatchdog.com reports editorially on Southwest Airlines' fares, but does so without using any "automatic device." Instead, we just use real live human researchers to see what they're offering on any given route on any given day.