The American Petroleum Institute (API) described the density of various petroleum products.
Reference temperature: 60°F (15.5°C)
specific gravity of the oil =
= (density of oil) / (density of water)
API gravity =
= (141.5 / (specific gravity of oil)) - 131.5
specific gravity of oil =
= 141.5 / ((API gravity) + 131.5)
