The chemical generation of superoxide ion (O2•−) by dissolving potassium superoxide was investigated. The chemically generated O2•− was then used to study the long-term stability of O2•− in dimethyl sulfoxide (DMSO) containing ionic liquids (ILs) and determine the rate constants based on pseudo 1st- and 2nd-order reactions between the IL and O2•− generated in DMSO. O2•− was unstable in DMSO containing [S222][TFSI], [DMIm][MS], [BDMIm][TfO], [EMIm][TFSI], [EMIm][MS], [P14,666][TPTP], [P14,666][TFSI], and all pyridinium-based ILs. In contrast, O2•− was very stable in DMSO containing [MOPMPip][TFSI], [BMPyrr][DCA], [BMPyrr][TFSI], [BMPyrr][TfO], [HMPyrr][TFSI], [MOEMPip][TPTP], [BMPyrr][TFA], [N112,1O2][TFSI], and [MOEMMor][TFSI]. This shows that these ILs can be used for different applications involving O2•−. The reaction rate constant, total consumption, and consumption rate of O2•− were determined. The rate constants of O2•− in some ILs were found to follow pseudo 1st-order reaction, while in others, pseudo 2nd-order reaction kinetics were observed.