He was undrafted despite an impressive career at the University of Iowa. In 2001, Evans led the nation in free throws attempted, free throws made, and double-doubles. He led the Big Ten Conference in rebounding in 2001 and 2002, and was named Big Ten Tournament MVP in 2001 and Second Team All-Big Ten in 2002. He signed with the Sonics as a free-agent, where he became known for his tenacious rebounding. In 2004-05, he led the league in rebounds-per-minute-played after finishing in the top 10 the two previous seasons. Despite playing under 24 minutes per game, he finished ninth in the NBA in total rebounds. A 2005 statistical analysis published on ESPN.com determined that on average, Evans will collect one quarter of all rebounds available while he is in a game.
Evans made the news on December 6, 2005, when he was absent for the opening minutes of the second half in a loss to the New York Knicks. Circumstances did not allow Evans to take a steroid test prior to the game, so a league official required that it be done at halftime. Evans laughed off the suggestion he was under suspicion. "I've been clean since I've been in the league. I've been clean since I've been in college. I've been clean since I've been in high school, middle school, elementary school. I'm just cleaner than clean. I'm cleaner than Pine-Sol."
For his rebounding prowess, Sonics fans refer to him as "The Collector," although some prefer the moniker "Pine Sol."
Evans's best statistical season was arrested on January 3, 2006, when the Sonics front office dismissed Head Coach Bob Weiss and promoted Assistant Bob Hill to replace him. In Hill's new system, Evans lost his starting spot and his minutes were drastically reduced. Following the first four games under Hill, Evans took a brief leave to attend the funeral of his girlfriend's mother. He remained incommunicado for several days. Upon his return, Evans saw limited action in but seven of the next fourteen games, during which time Evans, through his agent, requested to be traded to another team. On February 26, 2006, the Sonics traded Evans to the Denver Nuggets. In his first five games with the division-leading Nuggets, Evans played more minutes than he did in his final twenty-one games with the cellar-dwelling Sonics.
During a 2006 first round playoff game, Reggie Evans was accused of grabbing and groping Los Angeles Clippers center Chris Kaman in the testicles. This led Evans to be pushed on the floor. Kaman was quoted as saying "I felt I got a little violated by another man" . Evans was fined $10,000 but not suspended for his actions.