Carbon dioxide (CO2) was shown as a promising alternative for oil sands tailings treatment with economical and environmental benefits. This thesis aims to understand the role of CO2 addition in settling and densification of oil sands tailings. In this study, CO2 was pressurized into two industrial whole tailings. The optimal initial settling rate, supernatant clarity and solids content of sediment were achieved at CO2 partial pressure of about 100 kPa. Increasing the processing temperature improved the effects of CO2 on the settling of tailings. The improvement on settling and densification of tailings by CO2 was mainly attributed to pH reduction, which led to a decrease in the value of zeta potential of the fines. On the other hand, CO2 bubbles formed by dissolved gas under super-saturation pressure caused a less clear supernatant by disturbing the formed sediments. The limit of CO2 sequestration by oil sands tailings was experimentally evaluated.