Wikipedia says there are an estimated 268 billion barrels in Saudi Aramco's proven oil reserves, with maybe 90 billion more undiscovered. It produces somewhere between 3 and 4 billion barrels annually. If a barrel of oil is worth about $50, then the total value of Aramco is about $18 trillion. We can put a discount on that for time, but you might also want to consider that oil will get more difficult to pump out of the ground and price should increase faster than inflation. CPI is pegged to the price of oil, so all this stuff gets complicated.
Mind you, that estimate has remained unchanged since the late 80s, even though about 100 billion barrels have been extracted since then. OPEC quotas are based on a country's reserves. Take with a lot of salt.
The problem with that valuation is the fact that the IPO shares won't have any rights to the oil reserves. The devil is in the details. I'm sure most people buying stock think that they're buying part of SA's riches, but you're really only buying into the poorly run service company that extracts it.
What's odd is that they are talking about selling the stake when oil prices are near record lows. The other worrying point is that if Saudi is selling their oil production, why on earth would you want to be a buyer?
Typo in the parent - their Sovereign Wealth fund has assets of ~$700 billion. Though they've been using it heavily to prop up state spending with the collapse in the oil price and war in Yemen.
