Major differences which exist between terrestrial mid-ocean ridge basalts (MORB's) and lunar mare basalts reflect the different planetary characteristics of Earth and Moon. MORB's are enriched in aluminum and have higher Mg/(Mg+Fe2+). These features reflect a more aluminum and magnesium-rich mantle source for MORB's. Mare basalts are depleted in sodium and potassium relative to MORB's and, consequently, mare feldspars are depleted in the albite component relative to MORB feldspars; these features are a reflection of the alkali depleted nature of the Moon relative to the Earth. The oxygen fugacities that obtained during MORB petrogenesis follow the quartz-magnetite-fayelite buffer curve very closely while those of mare basalts are several orders of magnitude lower. This results in reduced valence states for Fe, Cr and Ti in mare basalts, which, in turn, has a significant effect on mineral-melt partitioning.