There are significant inconsistencies in the literature regarding the partition coefficient of phosphorus in olivine. This indicates that there may be a problem with the methods for determining this value. In this study, olivine phenocrysts from the Sequeiros Transform Zone were measured for phosphorus to determine the issues and constrain a more accurate value. The measured values range over several orders of magnitude. Estimates of phosphorus diffusivity in a basaltic melt are slower than some estimates of olivine growth rate, and this may mean that this spread is in some part due to kinetic effects during crystallization. As it is difficult to separate these contributions from the true equilibrium value, an alternative approach to constrain this value is needed. Using a statistical approach, we find a maximum value of D=0.027 and a minimum value of D=0.0033.