A tool to analyze the water mass mixture in a water sample by calculating the contributions from the original water masses (the source water masses) to the sample. OMP is based on a simple linear mixing model that assumes all water mass properties undergo the same mixing processes, i.e. their mixing coefficients are identical. This allows their distribution is space to be determined via a linear set of mixing equations. Mathematically speaking, OMP is an inversion of an overdetermined system performed individually for each observation point. The source water type contributions for each data point are obtained by finding the best linear mixing combination in parameter space defined by temperature, salinity, oxygen, nutrients and other water mass properties that minimizes the resisuals in a non–negative least squares sense.