This document provides requirements and guidance on the selection, accuracy, installation, commissioning, calibration and verification of automatic tank thermometers (ATTs) in fiscal/custody transfer applications. The ATT is used for measuring the temperature of petroleum and liquid petroleum products having a Reid vapour pressure less than 100 kPa, stored in cargo tanks on board marine vessels (i.e. tankers and barges). This document is not applicable to the measurement of temperature in refrigerated storage tanks, or pressurized cargo tanks on board marine vessels, which is covered in ISO 8310.