Serena Williams Upstages Kim Kardashian with Her Bikini Shots on Instagram

Two of the most endowed women when it comes to a full behind, Serena Williams and Kim Kardashian show off their bikini bums on Instagram.

Kim Kardashian has been uploading some photos sunning in her Instagram account while spending the past few days vacationing in Mexico. Her close pal, the reigning queen of Best Bum, Serena Williams upstages the reality star by posting photos to the photo-sharing site while she is apparently having a blast on vacation in Croatia.

Serena gave her followers a peak of her bum and her svelte yet athletic shape while wearing tangerine top and red bikini bottom.

The tennis star shared a number of bootylicious photos of her unwinding on a boat trip with her friends. One photo highlights the sports star sunning and relaxing on a yacht with a breath-taking view of the ocean. On other snap, Serena's bum is shown afloat as she's swimming in the sea.

Two weeks ago, Serena was forced to quit her doubles match at Wimbledon with sister Venus Williams after she was hit by a virus.

'I really wanted to compete, but this bug just got the best of me,' Serena said in an emailed statement. The tennis star looks forward 'to returning to Wimbledon next year.'

Meanwhile, just last week, Kim uploaded some poolside selfies while she's on vacation in Mexico at the home of the Girls Gone Wild creator, Joe Francis.

Kim shared a snap while sunbathing with Abbey Wilson, Joe's pregnant girlfriend, with hashtag #OurLovelyLadyLump. Then just recently, Kim uploaded throwback beach photo in Thailand with caption: "Flashback to Thailand! Did you guys like tonight's KUWTK episode in Thailand? #photoshoot #selfies."

The reality star was also seen accompanied by husband Kanye West and daughter North as they enjoyed some family time together by the beach in Puerto Vallarta, Mexico.