Dallas Love Field has 20 gates. They are legally forbidden to build more. (Thanks, Congress!)
Southwest has 16 gates. They’ve subleased 2 from United. That’s 18. The other 2 gates are controlled by Virgin America.
Delta flies from the former United gates. There’s a big court battle over whether they’ll be able to continue to squat on those gates or not. And it all started with the federal government requiring American to give up its gates to Virgin America.