Supposedly, prices fall because colluding firms want to assuage calls for regulation and taxes. Anyone even remotely familiar with commercials, advertising low prices, knows how sloppy that argument is. There's no evidence of sustained collusion, because there's no way to enforce such deals. Prices rose due to sudden demand and are falling because this competitive industry is finally catching up.
This is not a new story. From Amity Shlaes' The Forgotten Man. In 1934,
[Harold Ickes] had discovered that at numerous points oil was being extracted clandestinely and illegally, outside his NIRA [National Industrial Recovery Act] production quotas, and sold at prices that undercut the policy to force prices upward. He was outraged and opened a campaign against the oil bootleggers, describing them as possessed of a "sly animal cunning." (p 203)No wonder oil CEOs are paid so much. It's not fun being the villain no matter what you do.