Techniques for measuring the pressure dependencies of the electrode potentials (characterized by the cell reaction volume ΔV cell ) and electrode kinetics (volume of activation ΔV ‡ ) of metal complexes are described. Volumes of reaction ΔV for net redox reactions can be obtained by the combination of ΔV cell values. We show how ΔV cell can be broken down into contributions of the couple of interest and the reference electrode, and how the solvational and intrinsic components of the former can be evaluated. Values of ΔV ‡ measured for electrode reactions of aqueous metal complex couples are precisely one-half of the ΔV ‡ found for the corresponding outer-sphere self-exchange reactions, and can generally be accounted for by an extension of Marcus theory developed for the latter. When ΔV is known, the theory can be extended to ΔV ‡ for redox ‘cross’ reactions; thus, ΔV ‡ can serve as a criterion of a simple, adiabatic, outer-sphere reaction mechanism.