Liquid petroleum as produced from the ground. Unrefined liquid petroleum. It ranges in gravity from 9°API to 55°API and in color from yellow to black. Its main usages are for transportation both road and air, for heating and as feedstock for the petrochemical industry. Global reserves of crude oil currently suffice for about 40 years, but more fields are discovered from time to time. There are hundreds of different types of crude oil, but the two most common and the most quoted in the press is Brent and WTI. The most important characteristic of crude oil is its API (a number that defines its relative gravity). The lower the gravity the higher the API number and thus usually the cost is higher because it includes a greater proportion of light components.