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 Economist