Oil is the most demanded natural resource after water. It is still the main source of fuel and is directly linked to the economic progress of the 21st century. Oil-rich nations use this as a social capital, capable of generating wealth and influencing global geopolitical dynamics. Oil is so important that price changes impact stock markets and cause large variations in financial market investments. Recent history shows that oil is a resource that is eventually used politically - as bargaining power - by the nations that hold it, as was observed in the OPEC cartel in the 1970s.