OSLO  - Norway's finance ministry asked the central bank on Tuesday to explain what impact a potential listing of state oil giant Saudi Aramco would have on the benchmark equity index of the country's $1 trillion sovereign wealth fund.

The request was made as part of public consultations on Norges Bank's proposal to drop the oil and gas sector from the fund's investments in order to reduce the risk of oil-price fluctuations. 

The Saudi government plans to sell about 5 percent of Aramco, hoping to raise some $100 billion or more in what would likely be the world's biggest initial public offering. 

"The company will own much larger petroleum reserves than oil firms that are currently listed, which will raise the risk from the return on (those) resources," the finance ministry said in a letter to the central bank.

"We're asking Norges Bank to explain the impact a listing of Saudi Aramco will have on the fund's benchmark index," it added.

The wealth fund's energy investments, including integrated oil companies, oil service firms and renewable energy, account for about 4 percent of the fund's value of around 300 billion Norwegian crowns ($38 billion), the letter said.

($1 = 7.8986 Norwegian crowns)

(Reporting by Nerijus Adomaitis, editing by Gwladys Fouche and Dale Hudson) ((nerijus.adomaitis@thomsonreuters.com; +47 9027 6699; Reuters Messaging: nerijus.adomaitis.thomsonreuters@reuters.net))