Stump Sparks

I like Sparks. I like him for a lot of reasons. A couple of those reasons are that he's wicked smart, and also he's good people (Andrea - I recognize that despite the "s", "Sparks" is singular, and people is plural, but feel free to comment). These two things are often mutually exclusive, so he's got that going for him. In my opinion, his forte in the world of wicked smartness is understanding cause and effect. He's like a cause and effect genius. If you name a cause, he can name the effect(s). And if you name an effect, he can name the cause(s).

So today I'm going to give Sparks an effect and ask him to explain the cause.

Effect: oil is trading in the neighborhood of $40 (down from the $150+ range earlier this year).
Cause: ???

I've always assumed that demand for this sludge is fairly constant and predictable, and that OPEC is at least somewhat influential in managing supply - so how can we have such a range over such a short period? It doesn't make sense to me. I can understand how other commodities produced in limited regions of the world and subject to new technologies / innovations might move quite a bit - but oil? Commentators seem to point the finger at speculating hedge funds, but that seems impossible to me - such a big market.

So, Sparks - what gives?