Saudi Aramco’s IPO will be historic, but no easy feat to pull off. The company’s sheer size and intertwining with state finances leave many key issues to be resolved ahead of a planned listing – notably concerning its oil reserves, tax regime and listing location. These make the planned 2018 timeframe ambitious.

Ever since Saudi Arabia’s Deputy Crown Prince Muhammad bin Salman captured the world’s attention in April 2016 by announcing plans to float up to a 5%...