Hyperinteresting quote from Southwest Airlines CEO Gene Kelly on whether the airline might add another destination in 2009:

We are interested in growing our route network. We are continuing to evaluate new city opportunities. There are a lot of cities that we don’t serve. I will certainly admit that we’re continuing to research very seriously all of those opportunities.

I think we’ve shown in 2009 that we can grow, even in this tough environment. So no, I’m not ready to say that Boston will be the last new city, but we haven’t made that decision yet.

Southwest has announced it will begin service this year to Minneapolis-St. Paul (began March 8), New York LaGuardia (June 28) and Boston (Aug. 16).

This leaves Atlanta, Charlotte, Cincinnati, Memphis, and Milwaukee as the largest markets it does not currently serve. The airline also does not fly to Miami, Newark, New York JFK, and Washington Reagan National but serves those areas via other airports in their respective metro areas.

Analysis: All the places they don’t serve have some sort of issue(s): slot/gate limits, delay-prone, expensive to operate from, and/or are other carrier’s hub. EWR/JFK/DCA would all depend upon being able to cut the right deal for access. Miami depends upon how much Southwest wants to be there and pay the associated higher operating costs (they have a fair number of flights from Ft. Lauderdale).

Of the markets they aren’t in, Atlanta and then Charlotte are the biggest holes. Cincinnati and Memphis both would make more sense — which is not the same thing necessarily as make sense — should Delta/Northwest take down their hub. That’s much more likely to happen in the short-term in Cincinnati than Memphis. CVG though isn’t that big a market and Southwest already captures some of those travelers via Louisville, Columbus, and Indianapolis. Milwaukee is just a bad fit, as its very near Chicago and AirTran is trying to establish a major presence there.

So the most likely places would be one of Charlotte, Atlanta, Newark, (less likely) Miami, or Cincinnati.