Abstract New quaternary graphite intercalation compounds (GICs) were synthesized by intercalation of lithium and sodium into ternary potassium-mercury GICs. X-ray diffraction showed that quaternary compounds have five-layer structures LiKHgKLi (in the case of lithium) and KHgNaHgK (in the case of sodium). The compounds were synthesized under non-equilibrium conditions. The interaction of ternary potassium-sodium-mercury alloys with graphite was investigated. The thermodynamical approach suggested shows that the third component of the alloy (in this case mercury) can determine the method of intercalation of binary alkali metal alloys in graphite. Moreover, a quaternary GIC with a five-layer structure of intercalant was synthesized by direct interaction of potassium-sodium-mercury alloy with graphite under equilibrium conditions.