The slick from the sudden fall in oil prices is spreading. Cheaper oil is good for the economy but investors face a risk of accidents as traders retreat from the expectation that the oil price would continue rising.

The most obvious casualties are energy stocks. Their share prices indicated that the stock market never believed the highest crude prices were sustainable. From crude’s brief dip below $50 a barrel in January last year, until its peak last month, it gained 183.5 per cent. Meanwhile, the S&P 500 energy index of US stocks gained only 43.9 per cent, and the MSCI World energy index rose only 29.7 per cent, in local currency terms.