Oussama "Ous" Mellouli (Arabic: أسامة الملولي; born 16 February 1984) is a Tunisian swimmer who competes in the freestyle and medley events.

He is a three-time Olympic medalist, is an African record holder, and trains with the USC Trojans team based at the University of Southern California, where he studied as a computer science undergraduate and swam collegiately.

On 19 February 2007, he broke his own African Record in the 200m individual medley for the fourth time since 2003 at the USA Swimming Grand Prix meet, held at the Mizzou Aquatic Center at the University of Missouri.

Three days later, on 28 March, he swam to the first Tunisian World Championship in swimming, winning the 800m freestyle in a then African Record of 7:46.95 — one of the top 10 fastest times ever.

Mellouli won 5 gold medals (200m and 400m individual medley, and 200m, 400m, and 1500m freestyles) at the XVI Mediterranean Games in Pescara, Italy.

[5] In July 2021, Mellouli had initially decided to withdraw from the 2020 Summer Olympics in Tokyo due to a dispute with the Tunisian federation for alleged forgery since 2017.

[6] However, he later announced that he would compete at the Tokyo Games, as the Tunisian Olympic Committee President Mahrez Boussian had promised to settle the dispute.

[7] On Wednesday, August 4, 2021, Tunisian swimmer Oussama Mellouli finished 20th in the 10 km open water marathon at the Tokyo Olympics.

A few weeks after the conclusion of the 2007 World Championships, reports began to surface that Mellouli had tested positive for a banned substance at the 2006 U.S. Open, 30 November – 2 December 2006.

These reports surfaced because FINA, the international governing body of the sport, had discovered that Tunisian authorities had known about the positive test but had only given him a warning.

He argued that he took the pill to help himself with writing a term paper (to sustain or enhance his academic performance) in the days leading up to the weekend US Open meet and that the drug was not intended as a performance-enhancing substance for competitive swimming.