Something to consider about oil, is that most of the time it hasn't really been a free market a such.
The Railroad Commission of Texas formally regulated prices 1930 - 1970, and by 1973 OPEC had stepped in to do essentially the same.
So over the past 85 years, there have only been 3 years when oil hasn't been under some degree of direct, reasonably coordinated efforts to control price. And nothing really happened in those 3 years anyway, the Railroad Commission didn't officially announce that they'd stopped regulating prices, they just lost the ability to effectively do it as US oil production peaked although even that wasn't recognised at the time, so we may as well say that it's been regulated since 1930 in a practical sense.
So in any discussion of oil prices, we are talking about a market where there has always (well, unless you want to go back pre-1930) been a single entity with the ability to raise prices, an most of that time the same entity has also had the ability to raise output and drop the market price should they wish to do so. That is manipulation of the market as such, in addition to direct price controls imposed by various governments over the years.
Thus far, nothing has changed. OPEC still exists, their largest member is simply choosing to over supply the market and drop prices. It may well be that OPEC never regains control, but thus far nothing extraordinary has happened in that regard. If the Saudi's really wanted oil at $100 then they would have no trouble doing so. Simply refuse to sell below that price, get the other OPEC members to do likewise, and they'll still find plenty of buyers.
I'm always wary of any market where government is the largest player. And if you look at who "big oil" actually is, it's not the likes of Exxon at all. It's governments which dominate the upstream industry in many of the major producing countries either directly, or via very close association with "private" oil companies.