Saudi Arabia slashed the tax rate paid by state oil producer Saudi Aramco, a key milestone in preparing the company for what may be the world’s biggest initial public offering. “The new tax rate will bring Saudi Aramco in line with international benchmarks,” Nasser said. The new rate is effective retroactively from Jan. 1. Deputy Crown Prince Mohammed bin Salman’s $2 trillion valuation, based on Aramco’s right to exploit the kingdom’s giant oil reserves, would see the sale raise $100 billion and dwarf Alibaba Group Holding Ltd. as the largest IPO in history. But others have said that valuation could be ambitious given uncertainty about oil prices, the future of fossil fuels and political risks in the Middle East. The tax cut will increase Aramco’s net income by 300 percent, potentially valuing the company at $1 trillion to $1.5 trillion, Sanford C. Bernstein & Co said in a March 28 report. Its per-barrel profit is expected to be in line with oil majors such as Exxon Mobil Corp., it said.