Partition coefficient
![An equilibrium of dissolved substance distributed between a hydrophobic phase (top yellow layer) and a hydrophilic phase (bottom green layer) is established in special glassware such as this separatory funnel that allows shaking and sampling from which the log P is determined.](/Images/godic/202502/01/Separatory_funnel_with_oil_and_colored_water2738.jpg")
![Drug permeability in brain capillaries (y-axis) as a function of partition coefficient (x-axis).[27]](/Images/godic/202502/01/Log_P_examples_012739.png")
In the physical sciences, a partition-coefficient (P) or distribution-coefficient (D) is the ratio of concentrations of a compound in a mixture of two immiscible phases at equilibrium. Hence these coefficients are a measure of the difference in solubility of the compound in these two phases.