The abundance of the alkali metals in 130 samples from the Gulf of Mexico was determined spectrographically. The results show that only a slight enrichment of rubidium with respect to potassium exists in the sediments while there is present a significant enrichment of cesium with respect to both potassium and rubidium. The potassium-sodium ratios indicate that these two elements are present in about the same proportions as in igneous rocks. The lithium abundance is similar to that found in igneous rocks. Thermal analyses suggest that rubidium is enriched with respect to postassium in the illite-rich sediments and that these sediments are relatively low in cesium. That a relatively high lithium content is associated with montmorillonite-rich sediments is also suggested. The alkali metal content of the sediments apparently does not vary systematically with depth below the present sedimentary interface or with distance from shore. In the sediments from the eastern part of the Gulf the distribution of all the alkali metals is similar. The results of the investigation suggest that much of the separation of the alkali metals and the enrichment of one with respect to another may occur during weathering and that the hydrated radii and ionic potential based on the hydrated radii are not the only factors which control the behavior of the alkali metals during the weathering and sedimentary cycles.