No two crude oil streams have exactly the same chemical makeup. Some are gooey and laden with impurities, most commonly sulfur, which can make up to 3 percent of the crude oil by volume. Such crudes are called “heavy sours.” Some, like Canada’s oil sands, are so heavy that they are solid at room temperature. Others are so pure they have the color and consistency of nail polish remover and are called “light sweets.”
