the answers to your first questions can be found here with a little persistence:
EIA - Petroleum Data, Reports, Analysis, Surveys
EIA - Petroleum & Other Liquids Data
As far regulating the speculators, not much, not much.
The DOJ "might" get involved but you'd have to be pretty big fish (and white).
Most of it is regulated the same as any other commodity that's traded on the NYME or such.
Now ponder this for a second:
suppose you were running a powerful country in the middle east that has a whole bunch of oil.
You're a major player in OPEC and don't really want to piss off the other members too much, and you really don't want to get caught manipulating the price of oil more than OPEC agrees to, but you secretly you want to stick it to the US.
So you produce and offer to sell your full quota of oil.
EXCEPT ......... an agent in europe who is secretly employed by you uses your money to buy your product and effectively take it off the market.
All you are doing is withholding oil to drive the price up but it doesn't look like that and the US gubmint doesn't catch on right away. They kinda know but they don't say anything because you're driving up the price also increases their revenue from the oil. You make more money, they make more money, only the US the people get screwed.
On paper is looks like there is a large surplus of available oil but in reality those numbers have been doctored. The supply isn't as big as it seems and the market acts in a way that would indicate a smaller supply than the numbers say. Sound familiar so far?
Then after a few months when the price has jumped a whole bunch, you dump the oil at a much higher profit.
Then because you are so smart and have so much power, you short the market right before you sell off your inventory, and make a killing as you drive the price down. But it looks like someone else is doing it and you laugh all the way to the bank with your $ trillions and no one says squat.