The NCAA Division I Football Bowl Subdivision (FBS), formerly known as Division I-A, is the top level of college football in the United States. The FBS is the most competitive subdivision of NCAA Division I, which itself consists of the largest and most competitive schools in the National Collegiate Athletic Association (NCAA). As of 2018, there are 10 conferences and 130 schools in FBS. College football is one of the most popular spectator sports throughout much of the United States, and the top schools generate tens of millions of dollars in yearly revenue. Top FBS teams draw tens of thousands of fans to games, and the ten largest American stadiums by capacity all host FBS teams or games. College athletes are not paid, but colleges are allowed to provide players with non-monetary compensation such as athletic scholarships that provide for tuition, housing, and books. Unlike other NCAA divisions and subdivisions, the NCAA does not officially award an FBS football national championship, nor does it sanction a playoff tournament to determine such a champion on the field. Instead, organizations such as the Associated Press and AFCA have historically sought to rank the teams and crown a national champion, by taking a vote of sports writers and coaches, respectively. In place of such a playoff, various cities across the United States hold their own post-season contests, called bowl games, in which they traditionally invite teams to participate in them. Historically, these bowl games were mostly considered to be exhibition games involving a payout to participating teams. However, in the modern era they are considered the de facto post-season. There have been agreements in recent decades (such as the Bowl Coalition from 1992 to 1994, the Bowl Alliance from 1995 to 1997, the Bowl Championship Series from 1998 to 2013, and the College Football Playoff from 2014 to the present) by the premier FBS conferences and bowl games to organize matchups so that the FBS national championship is decided on the field.