My understanding is that it was hydraulic fracking that made the difference.

See, the 'peak oil' people were wrong; turns out that if you are willing to pay more, there's a lot more oil you can extract (albeit at a higher cost)

I actually think it was a self-defeating prophecy in a way. The peak oil folks actually had some mindshare for a while, and there was a lot of investment in more expensive ways to get oil out of the ground that had the assumption of long term oil prices being over a hundred bucks a barrel. This, I think, caused over-investment in new ways of extracting oil, which drove up production and drove down prices. (I mean, there was also a lot of investment in renewables, and I imagine that is also putting downward pressure on oil prices.)