According to an NHL source, the contract is worth $4.167 million per season.
Klefbom, the No. 19 overall pick in 2011, has only played in 77 career NHL games and has registered 23 points in that time. His signing follows a trend of teams locking up young defenseman to long-term contracts even before players fully prove themselves at the NHL level.
He had 20 points, including two goals, in 60 games last season. He ranked second among Oilers defensemen in points (20) and time on ice (21:59), setting career highs in both categories. He also ranked third among Oilers defensemen in blocked shots (102).
The Karlstad, Sweden, native has also represented his country several times internationally, most recently at the 2015 world championship. He also captured a gold medal with Sweden at the 2012 world juniors.
The Associated Press contributed to this report.