British Thermal Unit or BTU 12 : The amount of heat input required to raise the temperature of one pound of water by 1oF at water's maximum density at 39oF. It is approximately equal to 1 kilojoule
George E. King Engineering, 5000 Oilfield Terms: A Glossary of Petroleum Engineering Terms, Abbreviations and Acronyms, US 2010. http://gekengineering.com/Downloads/Free_Downloads /Glossary_of_Petroleum_Engineering_Terms_25_August _2010.pdf, (Oil - Amer) {593}