The solubility of carbon dioxide in the room-temperature ionic liquids 1-butyl-3-methylimidazolium hexafluorophosphate and 1-ethyl-3-methylimidazolium tetrafluoroborate for temperatures ranging from (303.2 to 343.2) K and pressures below 5 MPa were measured using a thermogravimetric microbalance. The gas solubilities were determined from absorption saturation (equilibrium) data at each temperature and pressure. The buoyancy effect was accounted for in the evaluation of the gas solubilities. An accurate equation of state and density equation for carbon dioxide and ionic liquids, respectively, were employed to determine the effect of buoyancy on the gas solubilities. The carbon dioxide solubilities in ionic liquids are presented as a function of temperature and pressure. The experimental solubility pressure data of carbon dioxide in the ionic liquids was successfully represented using an extended Henry's law correlation.