Pollstar, the 39 dates in North America grossed $38.3 million with 423,017 tickets sold. Worldwide, the Femme Fatale Tour was the eleventh highest-grossing tour of 2011, with a gross of $68.7 million. 697,957 fans attended the shows worldwide, with an average attendance of 8,724, paying an average of $98.43. Background In an interview on Ryan Seacrest's radio show on March 4, 2011, Spears stated she would tour the United States in the "early summer" in support of Femme Fatale. On March 29, 2011, following her performances on Good Morning America, she announced a co-headlining tour with Enrique Iglesias, starting in June 2011. Hours after the announcement, it was reported by Billboard that Iglesias had pulled out of the tour. Ray Wedell of Billboard speculated that the reason may have been that Spears was deemed by news outlets as the headliner, while Iglesias was considered the opening act. The first twenty-six North American dates were also announced on March 29, 2011. The opening acts were announced on April 12, 2011. Spears stated, "This is the Femme Fatale tour and I'm thrilled to have Nicki Minaj, Jessie and the Toy Boys, and Nervo join me and get everyone on the dance floor. Can't wait to take the Femme Fatales on the road." Tickets for select markets went on sale on April 30, 2011, at ticket seller Ticketmaster and tour promoter Live Nation's websites. In May 2011, it was announced that Spears would headline Summerfest on July 9, 2011, at the Marcus Amphitheater in Milwaukee. She previously headlined the festival on July 8, 2000, during the Oops!... I Did It Again Tour, and had to cancel her performance during The Onyx Hotel Tour in 2004 due to a knee injury. Summerfest's entertainment director Bob Babisch said, "It's going to be a great dance party. [...] This is going to be the biggest production we've ever put in the Marcus Amphitheatre. There's a thrust that goes out on the stage about 80 feet, and it's about 80 feet wide, and there's all kinds of things flying in and out." The European tour dates were announced on her official website on June 5, 2011. On July 25, 2011, Spears announced through her Ustream page at 18:00 EST (23:00 UTC) a South American leg of the tour. Accompanied by two of her dancers — one translating in Spanish and the other in Portuguese — she also