It was not long ago that $100 per barrel oil was accepted as the new normal. China's strong economic growth (and energy demand) would continue apace, and OPEC and Saudi Arabia would continue to play the traditional role as swing producer in support of oil prices. Events have proved otherwise.
Oil markets have entered a new period. Now it is supply, not demand, which is the key the factor, making not-so-distant discussions of "peak oil" seem very far gone. China's economy, while still growing, has slowed. And by leaving oil prices to the market, OPEC has effectively ceded the role of de facto swing producer to a country that hardly expected it—the United States.