Sweet crude oil is a type of petroleum. Petroleum is considered "sweet" if it contains less than 0.5% sulfur, compared to a higher level of sulfur in sour crude oil. Sweet crude oil contains small amounts of hydrogen sulfide and carbon dioxide. High quality, low sulfur crude oil is commonly used for processing into gasoline and is in high demand, particularly in the industrialized nations. "Light sweet crude oil" is the most sought-after version of crude oil as it contains a disproportionately large amount of these fractions that are used to process gasoline (naphtha), kerosene, and high-quality diesel (gas oil). The term "sweet" originated because the low level of sulfur provides the oil with a mildly sweet taste and pleasant smell. Nineteenth century prospectors would taste and smell small quantities of the oil to determine its quality.