Liquid-liquid extraction based on reversible chemical complexation is a novel separation technique that is highly effective and selective for separation of polar organic solutes from aqueous solutions. Equilibria of aqueous solutions of glyoxylic acid, glycolic acid, acrylic acid, and benzoic acid with trialkylphosphine oxide (TRPO) in kerosene were investigated. Equilibrium concentrations are given at 298 K. An extraction equilibrium model was used to describe the experimental data. The equilibrium constants were evaluated. Loading of TRPO was calculated.