(The Economist) Along with bank runs and market crashes, oil shocks have rare power to set monsters loose. Starting with the Arab oil embargo of 1973, people have learnt that sudden surges in the price of oil cause economic havoc. Conversely, when the price slumps because of a glut, as in 1986, it has done the world a power of good. The rule of thumb is that a 10% fall in oil prices boosts growth by 0.1-0.5 percentage points.

In the past 18 months the price has fallen by 75%, from $110 a barrel to below $27. Yet this time the benefits are less certain. Although consumers have gained, producers are suffering grievously. The effects are spilling into financial markets, and could yet depress consumer confidence. Perhaps the benefits of such ultra-cheap oil still outweigh the costs, but markets have fallen so far so fast that even this is no longer clear.

The new economics of oil

The world is drowning in oil. Saudi Arabia is pumping at almost full tilt. It is widely thought that the Saudis want to drive out higher-cost producers from the industry, including some of the fracking firms that have boosted oil output in the United States from 5m barrels a day (b/d) in 2008 to over 9m b/d now. Saudi Arabia will also be prepared to suffer a lot of pain to thwart Iran, its bitter rival, which this week was poised to rejoin oil markets as nuclear sanctions were lifted, with potential output of 3m-4m b/d.

Despite the Saudis’ efforts, however, producers have proved resilient. Many frackers have eked out efficiencies. They hate the idea of plugging their wells only for the wildcatter on the next block to reap the reward when prices rebound. They will not pack up so long as prices cover day-to-day costs, in some cases as low as $15 a barrel (see article ). Meanwhile oil stocks in the mostly rich-country OECD in October stood at 267 days’ net imports, almost 50% higher than five years earlier. They will continue to grow, especially if demand slows by more than expected in China and the rest of Asia. Forecasting the oil price is a mug’s game (as the newspaper that once speculated about $5 oil, we speak from experience), but few expect it to start rising before 2017. Today’s price could mark the bottom of the barrel.