Base pairs formed by the inosine nucleoside (I) play an important role in many physiological processes as well as in various DNA technologies. Relative stabilities and favored base pair geometries of free inosine wobble base pairs in aprotic solvents have been determined through (1)H NMR measurements at room temperature and at very low temperatures in a freonic solvent. As indicated by its significantly deshielded imino proton, the Watson Crick-type I. C base pair forms a remarkably strong NHN hydrogen bond. For the thermodynamically less stable I.A wobble base pair, two configurations of similar population coexist at 133 K in the slow hydrogen bond exchange regime, namely a Watson Crick(I) Watson Crick(A) geometry and a Watson Crick(I)-Hoogsteen(A)geometry. I.U base pairs are stabilized by two rather weak hydrogen bonds and are significantly disfavored over inosine self-associates in a low-temperature Freon solution.