CO2 transportation safety can directly affect the implementation of carbon capture, utilization and storage (CCUS) projects. The assessment of consequences of accidental release of supercritical CO2 are very important in the consideration of CO2 transportation safety. To ensure accurate prediction of the consequence of an accidental CO2 release, the near-field source terms including thermo-hydraulics have to be investigated, as the near-field jet flow structure significantly affects the evolution of solid CO2 particles. The aim of this work is to understand the under-expanded jet structure and thermo-hydraulics characteristics of supercritical CO2 releases from pressure vessels or pipelines. Experiments were developed to carry out controllable CO2 release from a high pressure vessel. The under-expanded jet structure of supercritical CO2 was recorded by a high speed camera. The jet velocity was measured using differential pressure sensors and a hot wire anemometer. In addition, the jet temperature, CO2 concentration, pressure and mass flow rate were also monitored. Through varying the release orifices in the experiment, the effects of size and pattern of the release orifices were analyzed. (C) 2018 Elsevier Ltd. All rights reserved.