The phrase "barrel oil" refers to the unit used to measure and trade crude oil. It simply means the quantity of oil contained in a standard-sized barrel, which is about 42 gallons or 159 liters. Full definition
It may make sense for some producers to shut down in a $ 40 per barrel oil price environment. (investopedia.com)
My predictions of steadily rising oil prices over the last decade, including my call for $ 100 - per - barrel oil by 2007, had flown in the face of conventional wisdom. (jeffrubinssmallerworld.com)