The log P is usually defined as the equilibrium concentration ratio of the neutral state of a substance between two phases: log = log 10 ow = log [unionized solute] octanol [unionized solute] water Strictly speaking, this definition of the partition coefficient P as a thermodynamic equilibrium constant is independent of total solute concentration in the infinite dilution limit only. This reference state is commonly assumed in physics-based prediction models. The log P prediction challenge explores how well current methods are able to model the transfer free energy of molecules between different solvent environments without any complications coming from predicting protonation states.