Free-fatty acids are an essential component of biological systems and important in the structure of certain biological membranes. As a first step towards the study of self-assembly membrane lipids, coarse grained models of fatty acids have been developed. Coarse-grained models allow molecular simulations to be performed on larger spatial and temporal scales than is possible through atomistic simulation and are necessary to study the self-assembly of mixed lipid systems. We have developed a coarse-grained force field for fatty acids, using the RPM method formulated by Reith, Pütz, and Müller-Plathe [1, 2]. The RPM method allows for the radial distribution function of the coarse-grained molecule to match its atomistic counterpart, and so indirectly matches the structural properties of the coarse-grained model to its atomistic equivalent. Results will be presented for a number of pure and mixed lipid systems to demonstrate the suitability of the proposed force field for modeling crystalline and melt fatty acid phases as well as the transferability of the coarse-grained potentials.