Oil and gas reserves have fuelled the economic expansion of the world for over a century. However, oil and gas are finite natural resources, and as such are subject to depletion. The remarkable oil-driven chapter of history is half over. The second half of the oil age will be marked by economic contraction, and a transition threatened by great tension. It is an important issue with far-reaching economic, social, financial and political consequences. But it is a complex topic, and the data needed for proper analysis are far from reliable. This article written in 2014 provides a useful background with which to analyse the unfolding recent events that affect the world, not all of which were foreseen in detail.