A high-precision chromatograph has been used for determination of differential thermodynamic quantities of two gas-liquid systems. Individual α values and consequently Δ(ΔH°) were determined with a precision of ±0.02%. The precision in the measurement of Δ(ΔG°) was ±0.2%. These values represent an order of magnitude improvement over the best previously reported data. Heats of adsorption of hydrocarbons on carbon black and silica gel were also determined with a precision of ±0.6%.