Saudi Arabia slashed taxes by more than a third for state oil producer Saudi Aramco ahead of what could be the world’s biggest initial public offering.

New rates reduce Aramco’s income tax rate to 50 percent from 85 percent, Chief Executive Officer Amin Nasser said in an emailed statement. The Saudi Arabian Oil Co., known as Saudi Aramco, plans to sell as much as 5 percent of the company in an IPO next year that the kingdom estimates could value the business at more than $2 trillion.

“The new tax rate will bring Saudi Aramco in line with international benchmarks,” Nasser said. The new rates on hydrocarbon companies announced by royal order on Monday are effective retroactively from Jan. 1, according to the official Saudi Press Agency.

Nasser said in January that Saudi Arabia will reduce the company’s overall tax rate to make the share sale more attractive to investors. Aramco currently pays a 20 percent…