Complications restructuring Saudi Arabia’s state-owned oil company and disentangling its finances from those of the government are slowing the march toward what is expected to be the biggest initial public offering in history.

The hotly anticipated listing of a minority stake in Saudi Arabian Oil Co., the kingdom’s corporate crown jewel, is now unlikely to happen until late 2018 at the earliest, and if foreign advisers have their way, won’t happen until 2019, according to more than a half-dozen people involved in the process.