THE proposed sale of 5% of Saudi Aramco is not just likely to be the biggest initial public offering (IPO) of all time. “It’s like Gibraltar selling the rock,” as one expert on Saudi Arabia’s oil policy puts it. The world’s biggest oil company keeps the House of Saud in power, bankrolled 60% of the national budget last year, and is a paragon of efficiency in an economy otherwise mired in bureaucracy. The elevation on June 21st of Muhammad bin Salman, the 31-year-old architect of the IPO, to crown prince is likely to add more momentum to a sale planned for the second half of 2018.