It must earn eye-watering returns while speeding the shift to a post-oil economy. : About a decade ago, a flashy, deep-pocketed investor made an appearance. Saudi Arabia’s Public Investment Fund (PIF) had a mandate to go big, and was ready to: it picked up a $3.5bn stake in Uber, placed $45bn in the world’s largest technology-investment fund, SoftBank’s Vision Fund, and provided half the capital for a $40bn infrastructure fund run by Blackstone, a private-equity giant. It has since bought stakes in everything from Heathrow Airport and Nintendo to Hollywood studios and French hotels.