Abstract– Fourteen major basaltic units in Mare Serenitatis have been identified and mapped from differences in TiO2 wt%. The ages of these units have been inferred from their crater densities and reference to isotopically dated Apollo samples. It has been found that FeO and TiO2 wt% of the units do not show any apparent trend with time. However, the oldest units have much greater variation in FeO and TiO2 wt% than younger ones. No lateral trend in the age of the basaltic units is apparent within the basin. A vertical profile of Mare Serenitatis has been produced based on the depth of basalt within impact craters. The minimum depth of basalt has been estimated where craters have not exposed underlying highland material. The profile has been used to estimate the minimum volume of basalt within the basin to be ≈500,000 km3.