Diisopropyl naphthalenes (DIPNs) have distinctive mass spectra, including a base peak at m/z 197 and M+. at m/z 212 and, on the apolar columns typically used in organic geochemical applications, are resolved into five main peaks, although there are ten possible isomers. DIPNs have been recognised in rock matrix and solid bitumen samples from Oklo (Gabon) and subsurface samples of Silurian-Devonian clastic sediments from southern Tunisia (borehole MG1, Ghadamis Basin). They have synthetic/anthropogenic origins and are used as plant growth regulators and in the manufacture of printed paper. The most likely source of the DIPNs in these organic geochemical samples is tissue paper used to wrap the samples. It is suggested that they are preferentially adsorbed by solid bitumen and so are not released during solvent extraction of surfaces. Although they have been reported in environmental and food samples, this appears to be the first report of their occurrence in organic geochemical samples.