Advanced energy systems propose use of supercritical fluids (SCFs) as working fluids owing to various advantages associated with SCF. Supercritical water (SCW), supercritical carbon-dioxide (SC–CO2), and supercritical helium (SC–He) find proposed applications in advanced nuclear reactor designs too. Heat transfer behavior of SCFs is still not understood completely. Though there exist many heat transfer correlations and criterion in the literature, they miss having a general consensus among them. In spite of having many reported studies in literature for SCFs under forced convection conditions, studies related to SCF under natural circulation (NC) mode are very limited. In the present study, extensive experiments have been performed with SC–CO2 under NC conditions in tube geometry. The experimental data generated for vertical heated test section at various pressures between 8.0 and 13.0 MPa have been utilized to bring out salient findings related to fluid flow and heat transfer. The data have also been utilized to make comparison with generalized NC flow correlation available in the literature. Besides, few popular heat transfer correlations have been compared with experimentally obtained heat transfer coefficients.