We can see that PPUE for most regions peaked around 2000. The big exceptions being Canada in 1992 and Europe and Africa in the mid 2000s. What this means for the majority of the world is that in little over ten years the average number of barrels of oil a single rig produces has almost halved. Put another way oil companies have had to double the number of rigs in operation just to maintain oil production at 2000 levels. This is the very definition of drilling faster just to stay still.
~ Andrew McKay
One way to gauge the cost/effort of producing oil is via Production Per Unit Effort (PPUE).
“Peak oil” is not simply about the quantity of oil being produced; it is about the cost/effort of producing oil. For most of the history of petroleum production, the cost/effort was decreasing or steady. But now the cost/effort is increasing; That’s an inflection of the second derivative of the cost/effort versus production relationship.