RIYADH, March 27 (Reuters) - Saudi Arabia has set a range of income tax rates for producers of oil and hydrocarbons, the official Saudi Press Agency reported on Monday, quoting a royal decree.

The tax rate for investments exceeding 375 billion riyals ($100 billion) will be 50 percent, SPA said. It gave other rates for producers with smaller investments.

SPA did not say whether the announcement was directly related to national oil giant Saudi Aramco. Saudi authorities plan to sell shares in Aramco next year and have been considering whether to cut the effective tax rate on the company in order to facilitate the sale.

Aramco currently pays a 20 percent royalty and 85 percent tax to the government, Saudi officials have said.

(Reporting by Marwa Rashad and Reem Shamseddine; Writing by Andrew Torchia; editing by Sami Aboudi) ((andrew.torchia@thomsonreuters.com; +9715 6681 7277; Reuters Messaging: andrew.torchia.thomsonreuters.com@reuters.net))