Saudis have 200 years of oil left. Another scenario is oil becoming a minor source of global energy supply. The time horizon of both events is likely decades if not a century.
As soon as it ceases being an energy source for technology, it will transition into a food source for humans.
A barrel of oil contains 1.7MWh of energy, a grilled cheese sandwich is about 435 Wh of energy. A barrel of oil contains the equivalent of about 3900 grilled cheese sandwiches. At 80$/barrel, that is a 0.02USD per sandwich.
