From an AFL release

The 2011 Arena Football League regular season has been extended from 16 games to 18, Commissioner Jerry Kurz announced Monday.  The league will consist of 19 teams and each will play 18 regular season games, with the option of two preseason games. The change was passed in an ownership vote last week during the league's
Board of Directors meeting in Phoenix, AZ.
 
The AFL is adding teams in Philadelphia, Pittsburg, San Jose and Kansas City.