The recent Norway governments have spent much less than the return on the oil fund, which resulted in the return of 2,000 billion kroner (231 billion U.S. dollars) that remained unused, newspaper Aftenposten reported Saturday.

The very basic idea in the use of oil fund -- to use the return on investment, but let the fund itself remain untouched -- has not been followed at all, Aftenposten wrote.

Relatively low usage and several years of very high returns have thus yielded a total unused return of almost 2,000 billion kroner.

Only from 2012 to 2016, the return on the oil fund was 9.3 percent, calculated as the annual average. During the same period, Norwegian government annual average use was only 2.8 percent.

The result is that more than two thirds of the actual annual return has remained unused in the fund over these five years, Aftenposten wrote.

The fund has grown very quickly and amounted to 7,510 billion kroner at the end of 2016. This is more than twice as much as at the beginning of 2012.

"The fact that we have used less than actual returns so far gives us more space to spend money in a deep downturn in the future. It does not give us reason to spend more than the average return in the future," said Fredrik Wulfsberg, associate professor at Oslo and Akershus University College of Applied Sciences.

He added that the saved investment return will also provide a lasting return that should be used in future.

Until recently, the rule of action has been that the state should, in normal times, be able to use 4 percent of the oil fund in the state budget. It should correspond to expected real, long-term return.

"This would also lead to too high use of oil money in relation to the economy," Wulfsberg said.

Therefore, in order to ensure that the Norwegian economy does not "boil over," the use of oil fund has been much lower than 4 percent in the last ten years, with the exception during the 2009 financial crisis.

2016 was a historic year in oil money consumption, because the use of oil fund in the state budget was greater than the fresh oil money that came from the boreholes.

Still, the use of oil money in the state budget was much less than the return on the fund also in 2016, Aftenposten wrote. (1 U.S. dollar = 8.64 Norwegian kroner)