Klefbom, 18, was selected by the Oilers in the first round (No. 19) in the 2011 NHL Draft. He recently completed his second season in the Swedish Elite League in 2011-12, notching a pair of goals and four penalty minutes in 33 games played. Last season he made his professional debut at the age of 17, playing 23 games for the Elitserien champions Frajestad.
"We are very pleased with Oscar's growth over the past year since we drafted him last June," Oilers general manager Steve Tambellini said. "His development continues to improve. Oscar is a big puck-moving defenseman who has shown tremendous poise and ability playing in Sweden's top professional league, and particularly at the 2012 World Junior Hockey Championship in Alberta.
"We look forward to Oscar Klefbom wearing an Oilers uniform for years to come."
On the international stage, Klefbom led team Sweden to a gold medal at the 2012 World Junior Hockey Championship in Edmonton and Calgary and was named to the tournament's First All-Star Team. In 2011, he captained Team Sweden to a silver medal at the Under-18 World Hockey Championship.
For a third straight year, the Oilers possess the No. 1 selection at the NHL Draft, which will be held next Friday and Saturday at the Consol Energy Center in Pittsburgh.