Actually, the disposition of all of Iraq's natural resources (including oil) was not hidden. It's prominently included in the Constitution Iraqis were forced to adopt as the price of their "sovereignty."
There was opposition to the provisions and it was agreed that, in exchange for immediate ratification, the Iraqi parliament would make revisions to eliminate these odious provisions. No amendment to the Constitution has been proposed. Instead, there's been an effort to allocate the revenues from the sale of oil equitably and leave the ability to sell everything intact.
In fact, since the only thing that can be done with the oil is sell it to someone, that's not the most crucial natural resource destined for the auction block. Much more important is the future disposition of the land, water and forest resources of the country. (There had to be some practical reason for destroying water wells and pumping facilities in the Al Anbar outback during the initial invasion, thereby depriving three million sheep of the water they need to survive).
Saddam Hussein seems to have been into collectivized agriculture. Perhaps it was thought that it would be possible to move directly to industrialized agriculture.
On the whole, Iraq resembles nothing so much as 1980's American urban redevelopment writ large, without the niceties of eminent domain.