The Norwegian government said total revenues for the oil-rich economy were down by nearly 5 percent for the second quarter of 2015.

Statistics Norway, the government's data-recording agency, said total revenue for the second quarter of the year was $40.4 billion, down 4.7 percent from the same period last year.

"Sales revenue, transfers and the operating surplus from petroleum activities have all been reduced from the second quarter of 2014," the agency said in a statement.

The Norwegian government said its oil-driven economy has been pressured by lower crude oil prices, with overall investments expected to decline by 12 percent this year. Slow global growth leaves the government somewhat pessimistic, but an uptick is expected to emerge on the horizon.

German energy company Wintershall last week said it aims to spend as much as $1.8 billion in the Norwegian energy sector after the government signed off on its plans to develop the Maria prospect in the Norwegian Sea.

Tax revenue generated from the Norwegian oil and gas sector varies from year to year. For 2014, data show tax revenues generated from the sector was around $20.5 billion, which represented about 20 percent of total tax revenue for Norway.

Statistics Norway said investment in central government energy-sector activity was down by about $180,000 from last year.