"For the world as a whole, conventional crude output from existing fields falls from 69 mb/d today to 28 mb/d by 2035, meaning that about 40 mb/d of capacity (or more than 20 times today’s production of LTO) needs to be added over the projection period just to compensate for the effects of decline in conventional fields ... As discussed, adding unconventional oil into the equation does not have large implications for global observed decline rates, but it does increase the dependence of overall oil production on continuous investment ... In this case, the fall in production is even steeper, with oil output (excluding NGLs) dropping from 74 mb/d in 2012 to less than 13 mb/d in 2035, half of which would be from large onshore fields in the Middle East where decline rate are lowest ... Raising production (excluding NGLs) from 74 mb/d in 2012 to 80 mb/d in 2035 might appear to be a relatively modest undertaking, involving the addition of 6 mb/d. Once, though, it is understood that the actual requirement is to add close to 67 mb/d to reach the 80 mb/d target, both through net capacity additions and efforts to mitigate decline at existing fields, the scale of the task becomes clearer."

—IEA World Energy Outlook 2013, Kapitel 14, Seiten 469-470.