Aaness competed on the Norwegian national team from 1959 to 1965, and thus became part of the Norwegian speedskating revolution under the trainer Stein Johnson. His best season was 1962/1963, when he won silver at the Norwegian Allround Championships, skated a world record on the big combination one week later (in late January), became European Allround Champion in Gothenburg early February, and won bronze at the World Allround Speed Skating Championships of Karuizawa three weeks after that.
Nils Aaness had his best years alongside Knut Johannesen, and usually ended up a good number two after him. Aaness won a total of three silver medals and one bronze medal at the Norwegian Championships – every time behind Johannesen.
An overview of medals won by Aaness at important championships he participated in, listing the years in which he won each:
|Championships||Gold medal||Silver medal||Bronze medal|
Over the course of his career, Aaness skated one world record:
|Big combination||180.560||27 January 1963||Oslo|
To put these personal records in perspective, the WR column lists the official world records on the dates that Aaness skated his personal records.
|500 m||41.6||26 January 1963||Oslo||40.2|
|1,000 m||1:26.7||25 February 1964||Oslo||1:22.8|
|1,500 m||2:10.6||28 February 1960||Squaw Valley||2:06.3|
|3,000 m||4:35.0||25 February 1965||Oslo||4:27.3|
|5,000 m||7:42.8||26 January 1963||Oslo||7:45.6|
|10,000 m||15:54.9||24 February 1963||Karuizawa||15:46.6|
Note that Aaness's personal record on the 5,000 m was not a world record because Knut Johannesen skated 7:37.8 at the same tournament.
Aaness has an Adelskalender score of 179.158 points. His highest ranking on the Adelskalender was a second place.