Equal isn't always equal–even when, as in the tennis world, it's supposed to be that way.
In 1973, the U.S. Open became the first Grand Slam tennis tournament to award male and female players equal prize money. Tennis has certainly helped narrow the wage gap in sports: In 2015, seven of the top 10 highest-paid female athletes were tennis players. In some instances, like the U.S. Open finals in 2013 and 2014, the women's matches garnered higher TV ratings than the men's.
Still, despite earning equal prize money for winning tournaments ($3.5 million to this year's U.S. open champs), the top male players' earnings still outstrip those of most of their female counterparts. Men tend to receive more endorsement deals and sponsorships than women, and their matches are generally given more prominent TV slots and media coverage. What's more, some people–like BNP Paribas Open tournament CEO Raymond Moore, who said as much in March—still operate under the delusion that the men's game is more challenging and popular.
Read More: How to Watch the U.S. Open Without Cable
In honor of the U.S. Open, which kicked off this week, let's take a look at the wage gap between the highest-paid tennis players, ranked by the past year's earnings (data from Forbes):
Earnings: $7.7 million
Rank: 5th-highest-earning woman
The 26-year-old Czech player, a two-time Wimbledon champion, is known for her powerful left-handed groundstrokes. She has added to her prize money by endorsing Nike apparel and footwear, as well as Czech jewelry manufacturer ALO Diamonds. Earlier this year,, she was sidelined by a gastrointestinal illness. However, she came back to compete in Wimbledon, where she was knocked out in the second round, and the Olympics, where she earned a bronze medal. She'll also be competing in this year's U.S. Open.
Earnings: $23 million
Rank: 5th-highest-earning man
The Scottish star, a two-time Grand Slam champion, has reached at least the quarterfinals of every Grand Slam tournament he has participated in since 2011. He's also the two-time reigning Olympic champion, having defeated Roger Federer in 2012 and Juan Martin del Potro this year. Murray's earnings are augmented by a five-year, $30 million endorsement deal with Adidas, as well as a reported $25 million agreement with Under Armour that began in 2014. As the fifth-highest-earning man in tennis, his takeaways from the sport almost triple those of the fifth-highest earning female player, Petra Kvitova.
Earnings: $8.3 million
Rank: 4th-highest-earning woman
After winning the 2008 French open, the now-28-year-old Serbian player subsequently fell into a slump, failing to make a quarterfinal in her next 17 Grand Slam tournaments. In 2014, she rebounded by winning a series of smaller tournaments, including the Auckland Open and Aegon Classic, and is now ranked #25 by the Women's Tennis Association. She has added to her multi-million-dollar fortune by endorsing by Nike and Adidas; in 2006, she signed a lifetime contract with the latter.
Earnings: $33.5 million
Ranking: 4th-highest-earning man
The 26-year-old from Japan is ranked #6 by the Association of Tennis Professionals, the only Japanese male player to ever crack the top 10. His performance at the 2014 U.S. Open, where he was runner-up, made him the first-ever male player from an Asian country to make it to a Grand Slam singles final. He has endorsed the Wilson BLX Steam 99 racquet, and is sponsored by companies like TAG Heuer and Delta Airlines. Nishikori's earnings more than quadruple those of the fourth-highest-earning female player, Ana Ivanovic.
Earnings: $14.6 million
Rankings: 3rd-highest-earning woman
The 26-year-old Danish player held the #1 ranking from the WTA Tour for 67 weeks, the only woman from a Scandinavian country to do so. Since she began her professional career in 2005, she improved her year-end ranking each year until reaching the top slot in 2010 and 2011. She's also been a runner-up at the 2009 and 2014 U.S. Open championships. Her earnings have been bolstered by her role as an endorser for a line of Adidas tennis apparel designed by Stella McCartney. Recently, however, she's been hobbled by injury and has fallen out of the top 40 ranks.
Earnings: $37.5 million
Rank: 3rd-highest-earning man
Known as the King of Clay for his dominance on that playing surface, the #5-ranked player has won 14 Grand Slam singles titles. The 30-year-old Spaniard also took home the 2008 Olympic gold medal in singles tennis but could not defend his title in the 2012 Games due to a knee injury. He sat out this year's Wimbledon due to a wrist injury, but returned to competitive play in the Olympics, losing to Nishikori in the bronze-medal match. His earnings—bolstered by endorsements and sponsorships from companies like Kia Motors and Nike—are about 2.5 times greater than those of the third-highest earning female player, Caroline Wozniacki.
Earnings: $21.9 million
Rank: 2nd-highest-earning woman
The 29-year-old tennis pro achieved a #1 ranking for the first time at the tender age of 18. She has won five Grand Slam titles: once at each major tournament and twice at the French Open. Her career is known for its unusual longevity, despite her tendency toward injuries. However, Sharapova has recently been rocked by scandal. After admitting to testing positive for a banned substance at the 2016 Australian Open, she received a two-year ban from the International Tennis Foundation. The suspension also caused her to lose lucrative endorsement deals with Nike and Porsche, and allowed rival Serena Williams to surpass her in earnings. Sharapova won't sit idle during her ban, though: She announced this summer she will be enrolling at Harvard Business School.
Earnings: $55.8 million
Rank: 2nd-highest-earning man
The 29-year-old Serbian player is currently ranked #1 by the Association of Tennis Professionals—a spot he has held for 213 weeks. However, he's coming into this year's U.S. Open looking to redeem himself after a first-round loss in the Olympics earlier this month. During his career, he's won 12 Grand Slam titles, the fourth-highest in history. Djokovic has also earned millions in extra cash by endorsing companies like Adidas and Uniqlo. His earnings are more than double those of the second-highest earning female player, Maria Sharapova.
Earnings: $28.9 million
Rank: highest-earning female player
Williams, currently ranked #1 by the Women's Tennis Association, is considered by some to be the greatest female player of all time. She's won 22 Grand Slam singles titles, as well as 13 doubles titles with her sister Venus. She has endorsement deals with companies like Gatorade, Delta Airlines and Pepsi, and became a minority owner of the Miami Dolphins in 2009. Her efforts were also one of the driving forces behind the Wimbledon's decision to finally award equal prize money to male and female players. Williams is looking to redeem herself in this year's U.S. Open after losing to Italian player Roberta Vinci in the semifinals.
Earnings: $67.8 million
Rank: highest-paid male player
The 35-year-old Swiss tennis pro is currently ranked #4 by the Association of Tennis Professionals. He's won 17 Grand Slam titles throughout his career, including a record 10 in a row, from the 2005 Wimbledon to the 2007 U.S. Open. He makes the bulk of his earnings through endorsements of companies like Nike, Gillette, and Moet & Chandon. He earns more than twice what the highest-paid female tennis player, Serena Williams takes home.