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 / Updated By Jessica Spitz 
 
 Of the world’s 100 highest-paid athletes in 2018, not one was a woman. 
 
 Forbes released its annual list of top paid athletes on Tuesday, highlighting the monster earnings of superstars across all sports, with boxer Floyd Mayweather topping the list at $275 million. NBA players make up a majority of the list, followed by football and baseball players. 
 
 But 2018 was the first time in eight years that not a single woman has been included on the list — not even Serena Williams, one of the most accomplished and well-known athletes in history. She, along with fellow tennis players Maria Sharapova and Li Na, have made the list in recent years. 
 
 According to Forbes, Williams most likely lost her spot on the list because she had a baby last year, and therefore was unable to earn as much prize money as she has in years past. She was the top-earning female athlete in 2018 at $18 million, but fell nearly $5 million short of the $22.9 million cutoff for the top 100. 
 
 The pay gap in sports has been an especially pressing issue in recent years, as several women’s teams have initiated campaigns advocating for gender pay equity. The U.S. Women’s National Soccer Team has largely led the charge on this front, succeeding in securing a new collective bargaining agreement in 2017 after a year of arguing its case publicly. 
 
 The women had argued that players for the men’s national team earned far more than they did despite comparable work. 
 
 Around the same time, the U.S. Women’s National Hockey Team also reached an agreement with USA Hockey to end a wage dispute. 
 
 But, seeing as no women were able to clear the bar to make the Forbes top 100 list this year, the problem is clearly nowhere near solved, female athletes said. 
 
 Former soccer star Abby Wambach has devoted her retirement to advocating for equal pay in sports. In a recent speech at the Barnard College commencement, she noted that she and her male peers had “left it all on the field for decades with the same ferocity, talent and commitment." 
 
 "But our retirements wouldn’t be the same at all," she said. Referring to basketball star Kobe Bryant and quarterback Peyton Manning, she noted, "Kobe and Peyton walked away from their careers with something I didn’t have: enormous bank accounts.” 
 
 Several current and former athletes shared the lopsided statistics on social media. Tennis legend Billie Jean King, who broke barriers by pushing for equal prize money for women, said in a Twitter post: "Men, we need you to advocate as much for women as you do for other men. When more men in power become allies and care about gender equality, the power differential will shift." 
 
 Sports are a microcosm of society. Men, we need you to advocate as much for women as you do for other men. When more men in power become allies and care about gender equality, the power differential will shift. #HeForShe #EqualityForAll https://t.co/uaLVqJUDKQ — Billie Jean King (@BillieJeanKing) June 6, 2018 
 
 This is very sad.... and ppl say we are winning the war on equality, opportunity, and there is no such thing as a pay gap. https://t.co/BEdHUNqnTq — Kaillie Humphries (@BobsledKaillie) June 7, 2018 
 
 Canadian bobsledder Kaillie Humphries, an Olympic champion in 2010 and 2014, told NBC News that the lack of women on the Forbes list was frustrating. “There’s plenty of strong, powerful females that exist within our society that are high performance and demand excellence for themselves and what they do,” she said. 
 
 Humphries also said many of her male peers believe that the striking inequities in bobsleigh and other sports are acceptable, but that all athletes — not just female athletes — will need to recognize the pay gap as a problem going forward. 
 
 “I think talking about it is the first step. I think we were able to get to this position because of the females before us. You look at Billie Jean King. We were able to ride that wave for so long, and now we’re kind of at a standstill, and the conversation has stopped,” she said. “Hopefully [gender inequity] can become a global conversation so we can hold people accountable, and we can create change.” ||||| The best female tennis players in the world descend on New York City this week in advance of the U.S. Open, which kicks off on Monday. The top prize: $3.8 million for the women’s singles champ, the richest purse in tennis history. 
 
 The U.S. Open was the first tournament to offer equal prize money to men and women, in 1973, and tennis remains the prime outlet for the highest-earning female athletes, with eight of the top 10 slots. It is the one sport where earnings opportunities are at least in the same universe as they are for the men, as opposed to, say, basketball, in which average salaries in the NBA are 100 times their female counterparts in the WNBA. 
 
 Western & Southern Open - Day 4 2018 Getty Images 
 
 Despite the big prize money in tennis, the world’s top-earning female athlete received only $62,000 in winnings between June 2017 and June 2018. Serena Williams had a good excuse, though, as she took a 14-month break after revealing in January 2017 that she was pregnant. Her earnings of $18.1 million are still best among female athletes for the third straight year, thanks to an endorsement portfolio unmatched among women in sports. 
 
 Williams has more than a dozen sponsors, including Nike, Intel, Audemars Piguet, JPMorgan Chase, Lincoln, Gatorade and Beats. Only 16 athletes on the planet made more than Williams over the past 12 months from endorsements, and she made twice as much off the court as any other female athlete. 
 
 The Marketing Arm tracks the marketability of more than 4,500 celebrities through its Celebrity DBI, and Williams ranks among the top 1% of all celebrities because of a 91% awareness rate and high scores for aspiration and trust. 
 
 “She has a lethal combination as the best to play the sport and the story she has with Venus, breaking through as African-American tennis players,” says Matt Fleming, who runs the Marketing Arm’s practice of securing celebrities on behalf of brands and marketing campaigns. “Now, as a mother, it adds another layer of attractiveness from a marketers' standpoint.” 
 
 The Most Marketable Female Athletes 
 
 Celebrity DBI 
 
 The 10 highest-paid female athletes banked $105 million from prize money, appearances, royalties and endorsements in the 12 months ending June 1, 2018. The tally is down 4% from last year and 28% from five years ago. Blame the retirements of popular endorsement stars like Li Na, Danica Patrick and Ana Ivanovic. Another dent: The off-court income of Maria Sharapova, who was the top-earning female athlete for 11 straight years, is still down more than 50% after the fallout from her 16-month suspension for taking a banned substance. Sharapova ranks fifth this year at $10.5 million. 
 
 Caroline Wozniacki was widely considered the best player on the women’s tour without a Grand Slam title, but the former top-ranked player broke through at the Australian Open in January. The title was worth $3.1 million in prize money and pushed her total earnings, including off the court, to $13 million, second among female athletes. 
 
 Rounding out the top five are three more from the world of tennis in Sloane Stephens ($11.2 million), Garbiñe Muguruza ($11 million) and Sharapova ($10.5 million). The only non-tennis players in the top 10 are Indian badminton star P.V. Sindhu ($8.5 million) and racing's Patrick ($7.5 million). 
 
 1. Serena Williams — Total earnings: $18.1 million 
 
 Prize money: $62,000 
 
 Endorsements: $18 million 
 
 Williams launched her fashion collection, Serena, in May. After collections for HSN and Nike, this is her first solo compilation and includes dresses, denim and jackets. Her $86 million in career prize money is twice the total of her sister Venus, who ranks second all-time. 
 
 2. Caroline Wozniacki — Total earnings: $13 million 
 
 Day Three: The Championships - Wimbledon 2018 2018 Getty Images 
 
 Prize money: $7 million 
 
 Endorsements: $6 million 
 
 Her endorsement partners include Adidas, Rolex, Usana, Babolat and more. She partnered with Ovvo Optics this year for her own sunglasses line. The offerings include 11 men’s and women’s styles named after Wozniacki’s family, friends and fellow famous Danes. 
 
 3. Sloane Stephens — Total earnings: $11.2 million 
 
 Rogers Cup Montreal - Day 5 2018 Getty Images 
 
 Prize money: $5.7 million 
 
 Endorsements: $5.5 million 
 
 Stephens’ timing was impeccable for her first Grand Slam title (2017 U.S. Open): All of her sponsorship deals had expired or were set to run out at the end of 2017. The result was a huge bump in her off-court income thanks to new deals as a Slam winner with Nike, Mercedes-Benz, Rolex, Colgate, Chocolate Milk and Biofreeze. She was the first American woman besides the Williams sisters to win a Grand Slam since 2002. 
 
 4. Garbine Muguruza — Total earnings: $11 million 
 
 Nature Valley Classic - Day Four 2018 Getty Images 
 
 Prize money: $5.5 million 
 
 Endorsements: $5.5 million 
 
 Muguruza won her second Slam at Wimbledon last year. The title meant a big bonus from sponsor Adidas and also helped her land a deal with Rolex. Evian signed the Spanish-Venezuelan pro this year for a multiyear, global marketing campaign. Other sponsors include Babolat, Beats by Dre, Rolex, Maui Jim sunglasses and Caser Seguros insurance. 
 
 5. Maria Sharapova — Total earnings: $10.5 million 
 
 2018 French Open - Day Eleven 2018 Jean Catuffe 
 
 Prize money: $1 million 
 
 Endorsements: $9.5 million 
 
 Sharapova added a multiyear deal with UBS last year to a portfolio that already included Nike, Head, Porsche and Evian. The candy mogul expanded her Sugarpova brand via agreements with the Hudson Group and SBE Hotel Group. The brand is available in 22 countries, and sales should hit $20 million next year. 
 
 6. Venus Williams — Total earnings: $10.2 million 
 
 Day Three: The Championships - Wimbledon 2018 2018 Getty Images 
 
 Prize money: $4.2 million 
 
 Endorsements: $6 million 
 
 Alcon tapped Williams this year to help launch a new lubricant to combat dry eye. Her awareness level of 81% in the U.S. ranks behind only her sister’s among female athletes in the U.S. Williams, 38, is a popular draw on the speaking circuit, commanding as much as $100,000 for an appearance. She plans to play in the 2020 Olympics. 
 
 7. P.V. Sindhu — Total earnings: $8.5 million 
 
 Yonex Hong Kong Open Badminton Championships 2016 - Day 4 2016 On Man Kevin Lee 
 
 The Indian badminton player burst on the scene with a silver medal at the 2016 Summer Olympics. She was the first Indian female athlete to win a silver. The 23-year-old has a robust sponsor roster with Bridgestone, Gatorade, Nokia, Panasonic, Reckitt Benckiser and a half-dozen other brands. 
 
 Prize money: $500,000 
 
 Endorsements: $8 million 
 
 8. Simona Halep — Total earnings: $7.7 million 
 
 Western & Southern Open - Day 7 2018 Getty Images 
 
 Prize money: $6.2 million 
 
 Endorsements: $1.5 million 
 
 The world’s top-ranked tennis player had her deal with Adidas expire at the end of 2017. She reached the Australian Open final in January wearing a dress she designed herself. Nike inked the Romanian to a multiyear pact the following month. 
 
 9. Danica Patrick — Total earnings: $7.5 million 
 
 Monster Energy NASCAR Cup Series 60th Annual Daytona 500 2018 Getty Images 
 
 Salary/prize money: $3 million 
 
 Endorsements: $4.5 million 
 
 The most successful female race car driver moved away from full-time racing after the 2017 Nascar season and hung up her fire suit for good after the Indy 500 in May. She launched a clothing line, Warrior by Danica Patrick, last year and authored the fitness book Pretty Intense. Patrick has made headlines in the gossip magazines through her romance with star NFL quarterback Aaron Rodgers. Our earnings estimate includes six months of salary and winnings from the 2017 Nascar season. 
 
 10. Angelique Kerber — Total earnings: $7 million 
 
 Western & Southern Open - Day 5 2018 Getty Images 
 
 Prize money: $3 million 
 
 Endorsements: $4 million 
 
 Adidas is the biggest endorsement deal for the German tennis ace, and she also counts Generali, Porsche, Rolex, SAP and Yonex among her sponsors. Not included in Kerber’s earnings tally is the $3.3 million she pocketed for winning Wimbledon last month, after our counting period. 
 
 More Reading: 
 
 The World's Highest-Paid Athletes 
 
 Why No Women Rank Among The 100 Highest-Paid Athletes ||||| Story highlights Williams earned just $62,000 in prize money in the last year 
 
 Eight of top 10 athletes are tennis players 
 
 Earnings of top 10 down 28% from five years ago 
 
 (CNN) Even though Serena Williams won just $62,000 in prize money during the last 12 months the tennis great has still topped Forbes' list of the world's highest-earning female athletes. 
 
 The $18.1 million the 23-time grand slam champion earned in endorsements was enough for her to top the list for a third straight year despite not playing competitively for 14 months after revealing in January 2017 that she was pregnant with her first child. 
 
 The 36-year-old made twice as much off the court than any other female athlete, while only 16 male athletes have earned more than Williams over the past 12 months from sponsorships. 
 
 The top 10 females earned a combined $105 million from June 2017 to June 2018 -- down 4% from last year and 28% from five years ago. 
 
 In comparison, the combined earnings of the world's top 10 highest-paid sports stars, who are all male, tops a billion dollars. 
 
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– Women in sports say Forbes' annual list of the world's highest-paid athletes is proof that the gender pay gap is real and pressing. That's because—for the first time in eight years—not a single woman made the cut. The highest-paid female athlete in 2017—the year she gave birth to a daughter—was Serena Williams. Her $18 million puts her roughly $5 million below the take of the man to hold the 100th spot, Nicolas Batum of the Charlotte Hornets, who made $22.9 million, reports NBC News. "When more men in power become allies and care about gender equality, the power differential will shift," former tennis champ Billie Jean King says in a tweet. They top-earners for 2017 are: