The government controls its petroleum resources through a combination of state ownership in major operators in the oil fields (with approximately 62% ownership in Statoil in 2007) and the fully state-owned Petoro, which has a market value of about twice Statoil, and SDFI. Finally, the government controls licensing of exploration and production of fields. The fund invests in developed financial markets outside Norway. Spending from the fund is constrained by the budgetary rule (''Handlingsregelen''), which limits spending over time to no more than the real value yield of the fund, originally assumed to be 4% a year, but lowered in 2017 to 3% of the fund's total value.