In my study, I attempt to create a unique and more biologically relevant model of the cholesterol-rich exoplasmic leaflet of animal plasma membranes. Using electroswelling to create giant unilamellar vesicles, fluorescence microscopy, and the previously completed ternary mixture of DOPC, DSPC, and cholesterol, DOPC, a rare biological lipid, was gradually replaced with SOPC, an abundant biological lipid in order to create a partially completed quaternary phase diagram consisting of DOPC, SOPC, DSPC, and cholesterol. Focusing on the biological raft region, (Lo+Lα coexistence phase), reduction in the size of the coexistence region was found, thus verifying the notion that SOPC is more miscible with DSPC and cholesterol than is DOPC. DOPC replacements greater than 70% resulted in a disappearance of the coexistence region leading to a suspicion that the phase domains were too small to observe using optical fluorescence microscopy. The creation of a more biological model membrane can be used to further understand the role of lipids and proteins in cellular membranes as well as the size of biological rafts important in cellular function.