In this article, we evaluate the use of a novel single source Se_mS_n precursor for the synthesis of alloy PbS_xSe_1−x nanocrystals using oleylamine as stabilizing ligand, reagent and solvent. The precursor is prepared by quenching a stoichiometric melt of S and Se. We found that this precursor, like the related sulfur-oleylamine solution popular for the synthesis of metal sulfide nanocrystals, is tolerant of air and moisture and allowed for the simple and fast preparation of nanocrystals at relatively low reaction temperatures. The resulting nanocrystals were shown to form a homogeneous alloy using electron microscopy, elemental mapping, and powder X-ray diffraction with Vegard analysis. The precursor reactivity was studied with ⁷⁷Se NMR and Raman spectroscopy and was shown to form H₂Se and H₂S in situ in an analogous fashion to sulfur-oleylamine, which liberates H₂S.