While there are times when speculators clearly collude to drive up prices (e.g. the [link|http://en.wikipedia.org/wiki/California_electricity_crisis|California electricity crisis]), it's very difficult to do in a world market with so many producers and so many markets. California was different because electricity had to come in via existing transmission lines.
Oil is a risky commoditiy. It's essential for our industrial age and there are choke points (geographic and technological) that mean the prices can swing wildly (over a few years) even without speculation.
Outlawing non-approved buyers would be an invitation to an even larger underground economy in it. Do you really trust the government (made up of power hungry politicians who "need" campaign contributions, and overworked and understaffed regulators) to know what a reasonable price for oil is? I'm surprised.
My understanding is that most commodity traders eventually get out or go bust. In addition to correctly guessing which way the market will go, they have to know when to get in and get out. That's the tricky part and it's often ultimately guesswork.
Let's let the oil market work and punish those who break the law and manipulate it. Tax the profits and increase the taxes on use to drive down demand, but don't try to regulate the price.
My $0.02.
Cheers,
Scott.