Credit: Forbes

A glut of oil, the demise of Opec and weakening global demand combined to make 2015 the year of crashing oil prices. The cost of crude fell to levels not seen for 11 years – and the decline may have further to go.

There have been four sharp increases in the price of oil in the past four decades – in 1973, 1979, 1990 and 2008 – and each has led to a global recession. By that measure, a lower oil price should be positive for the world economy, with lower fuel costs for consumers and businesses in those countries that import crude outweighing the losses to producing nations.

But the evidence since oil prices started falling from their peak of $115 a barrel in August 2014 has not supported that thesis – or not yet. Oil producers have certainly felt the impact of the lower prices on their growth rates, their trade figures and their public finances butthere has been no surge in consumer spending or business investment […]