The pair featured in Sportico’s ranking, which listed basketball icon LeBron James as the highest earning athlete.
Osaka, who has equity in more than a dozen brands and endorsement deals with Nissan, Tag Heuer and Louis Vuitton, was ranked 20th.
Williams, who owns a venture capital firm and has long-standing partnerships with Pepsi, Gatorade and Aston Martin, was 52nd on the list.
A new study from SportsPro, using data from Forbes, has now compared the disparity between the top five highest-paid male and female athletes.
In SportsPro’s list, Paris Saint-Germain star Lionel Messi was named as the highest earner, making $130 million (£108 million) over the past 12 months.
This is in comparison to the $59.2m (£49.3m) earned by Osaka, meaning there is a 119.6 percentage increase between her pay and Messi’s.
The second highest-paid male athlete is James, who took home $121.2m (£101m). This is a 167.6 percentage increase on the $45.3m (£37.7m) earned by the second highest-paid female athlete, Williams.
Unfortunately, the percentage increase between the highest-paid male and female athletes gets greater as SportsPro moves down the list.
Ronaldo earned $115m (£95.8m) over the past 12 months, while Williams received $11.3m (£9.4m).
The fourth highest-paid male and female athletes are footballer Neymar and four-time Olympic gymnastics champion Simone Biles.
Neymar earned $95m (£79.1m) and Biles $10.1m (£8.4m), giving a percentage increase of 840.6%.
The greatest percentage increase – 954.5 percent – is between basketball star Steph Curry and tennis player Garbiñe Muguruza, who are the fifth highest-paid male and female athletes.
Curry made $92.8m (£77.3m), while Muguruza, winner of the lucrative WTA Finals, earned $8.8m (£7.3m).
It is significant that the majority of female athletes in the highest-paid list are tennis players – the sport arguably has more gender parity than any other, with Grand Slams giving equal exposure to male and female stars.