Abstract The solvation structure of O 2 − in deuterated dimethyl sulfoxide (DMSO) was investigated by analyzing the electron spin-echo modulation at 4.2 K. The analysis was carried out by Fourier-transforming the three-pulse echo modulation and by simulating the two-pulse echo modulation. The analysis indicates that each O 2 − interacts with two different groups of deuterium nuclei, each group containing six nuclei. It is found by simulating the modulation that one group is located at a distance of 0.25 nm from O 2 − with an isotropic coupling of 0.5 MHz while the second group is located at a distance of 0.35 nm with a negligible isotropic coupling. These results suggest a structure with each O 2 − solvated by two DMSO molecules arranged asymmetrically about the O 2 −. The two different distances appear to reflect the solvating molecule orientations with respect to the O 2 − bond.