Self-assembled lyotropic liquid crystalline lipid nano particles have been developed for a wide range of biomedical applications with an emerging focus for use as delivery vehicles for drugs, genes, and in vivo imaging agents. In this study we report the generation of lipid nanoparticle libraries with information regarding mesophase and lattice parameter, which can aid the selection of formulation for a particular end use application. In this study we elucidate the phase composition parameters that influence the internal structure of lipid nanoparticles produced from monoolein, monopalmitolein and pthytantriol incorporating a variety of saturated fatty acids (FA) With different chain lengths at varying concentrations and temperatures. The material libraries were established using high throughput formulation and screening techniques, including synchrotron small-angle X-ray scattering. The results demonstrate the rich polymorphism of lipid nanoparticles with nonlamellar mesophases in the presence of saturated FAs. The, inclusion of saturated FAs within the lipid nanoparticles promotes a,gradual phase transition at all temperatures studied toward structures with higher negative surface curvatures (e.g., from inverse bicontinuous cubic phase to hexagonal phase and then emulsified microemulsion). The three partial phase diagrams produced are discussed in terms of the influence of FA chain length and concentration on nanoparticle internal mesophase structure and lattice parameters. The study also highlights a compositionally dependent coexistence of multiple mesophases, which may indicate the presence of multicompartment nanoparticles containing cubic/cubic and cubic/hexagonal mesophases.