 Green Revolution techniques also heavily rely on agricultural machinery and chemical fertilizers, pesticides, herbicides, and defoliants; which, as of 2014, rely on or are derived from crude oil, making agriculture increasingly reliant on crude oil extraction.Proponents of the Peak Oil theory fear that a future decline in oil and gas production would lead to a decline in food production or even a Malthusian catastrophe.The effects of the Green Revolution on global food security are difficult to assess because of the complexities involved in food systems.