Crude oil is graded by its impurity content, which dictates the price. More impurities mean it's more viscous and sticky, like tar. Oil with low impurities is called 'light crude,' and oil with high impurities is 'heavy crude.' After the 1970s oil shock, the US started cutting down on Middle Eastern oil and ramped up imports from the Americas—Canada, Venezuela, and Mexico. The one they were most interested in was Venezuela.