ISO 19970:2017 specifies minimum requirements to quantify the boil-off gas (BOG) consumed on liquefied natural gas (LNG) carriers for their own functions, notably for power generation, during cargo transfer operations. BOG in this document refers to the low molecular gas returned from shore tanks to ships' tanks and the gas produced in ships' cargo tanks.

ISO 19970:2017 provides requirements for the metering of BOG and the subsequent calorific value calculations which can be taken into account when the energy transferred during cargo transfer is determined. This document also introduces performance requirements and calibration of the elements included in the BOG measurement system. A flowmeter of any type may be used to measure BOG as long as it meets the performance requirements specified in this document.

ISO 19970:2017, with some modification, can also be applied to the measurement of BOG consumed by LNG carriers at sea.