Activity coefficients at infinite dilution gamma(i)(infinity) of alkanes, alkenes, and alkylbenzenes as well as of the linear and branched C-1-C-6 alcohols, esters, and aldehydes in the ionic liquid 1-methyl-3-octyl-imidazolium tetrafluoroborate were determined by gas chromatography using the ionic liquid as the stationary phase. The measurements were carried out at different temperatures between 302 K and 396 K. Data points (204) have been obtained for 51 solutes. From the temperature dependence of the limiting activity coefficients, partial molar excess enthalpies at infinite dilution H-i(epsilon 1 infinity) of the solutes in the ionic liquid have been derived.