The first "Treehouse of Horror" episode aired on October 25, 1990 and was inspired by EC Comics Horror tales. Before "Treehouse of Horror XI", which aired in 2000, every episode was aired in the week preceding or on October 31; "Treehouse of Horror II" and "Treehouse of Horror X" are the only episodes to air on Halloween. However, due to Fox's current contract with Major League Baseball's World Series, every episode since has aired in November, with the exception of "Treehouse of Horror XX", which aired on October 18, 2009.