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Using multipulse techniques, principal values of the proton nuclear magnetic resonance (NMR) chemical shift tensors were measured at room temperature for the monoclinic form of oxalic acid, potassium hydrogen oxalate, and potassium hydroxide. The isotropic and perpendicular shifts of the first two compounds, which are of medium hydrogen bond strength, were found to fit the linear correlation with O···O distance, RO·O, established by Rohlfing, Allen, and Ditchfield for medium and strongly O–H···O hydrogen bonded solids. Although KOH is very weakly hydrogen bonded, the shifts were also found to conform to the correlation, at least as well as does the other data, thus extending this to weakly hydrogen bonded solids. An empirical correlation of the isotropic and perpendicular shifts with exp(-RO·O/ρ), where RO·O is in Å and ρ is 0.94 Å, is given here which has better agreement with the data and has an interpretation in terms of a simple ionic model of an O–H···O bond. [ABSTRACT FROM AUTHOR]