According to M. King Hubbert, peak oil is the point in time when the maximum rate of extraction of petroleum is reached. This will result in a terminal decline. Peak oil theory is based on the observed rise, peak, fall and depletion of aggregate production rate in oil fields over time. Some observers predict negative implications for the global economy following a post-peak production decline and oil price increase. This is rooted in the high dependence of most modern industrial systems on a high availability of oil. Predictions regarding the negative effects however vary greatly.
Oil production forecasts, on which predictions of peak oil are based, usually include optimistic and pessimistic scenarios. Optimistic estimations forecast that the global decline will begin after 2020 and they assume that major investments in alternatives will occur before a crisis - without requiring major changes regarding the lifestyle of oil-consuming nations. Pessimistic predictions of future oil production either stated that we already reached the peak or that it will occur soon.