Higher alcohols (C-4(+)) can be formed from ethanol via condensation pathways. collectively known as Guerbet reactions. Most prior Guerbet reaction studies involve vapor-phase reactions, with n-butanol yields typically no higher than 30% of theoretical. We report here condensed-phase Guerbet reactions of ethanol over Ni/gamma-Al2O3 catalysts modified by La2O3. Higher alcohol selectivities in excess of 80% at 230 degrees C and autogenous pressures are obtained in batch autoclave reactions. At these conditions, which are near the critical temperature of ethanol, the liquid phase is significantly expanded, byproduct gases (CH4 and CO2) are significantly dissolved in the liquid phase, and the vapor phase contains significant quantities of alcohols. To accurately compute ethanol conversion and product yields, both composition and quantity of each phase present at reaction conditions must be determined. To do this, the SR-Polar equation of state is combined with chromatographic analysis of liquid-phase samples taken during reaction to model the phase equilibrium in the reactor at reaction conditions. Composition, density, and total number of moles of the vapor and liquid phases in the reactor are determined from the model and analysis, and they are used to calculate more accurate values of conversion and product yield than those calculated by liquid-phase samples alone.