This paper addresses the role of solvent volatility on diameter selection of bicomponent polymer nanofibers produced via gas jet fibers (GJF) process whereby an axisymmetric turbulent gas jet is used for liquid jet initiation, liquid jet stretching, and solvent evaporation. Several morphological forms, such as interpenetrating network (IPN), bi-lobal, and core-shell are obtained by spinning homogeneous solutions of two immiscible polymers in two mutually miscible solvents. The diameter selection of fibers of the same morphology, e.g., bi-lobal, is achieved by spinning polymer solutions of two sets of solvents of different volatility. The results show that fiber diameter is strongly dependent on the value of vapor pressure of the solvents while the morphology is strongly dependent on the vapor pressure difference of the two respective solvents. The diameter selection by GJF process is most prominent for IPN nanofibers, moderately prominent for core-shell fibers, and almost indifferent for bi-lobal nanofibers. The relative rates of solvent evaporation are useful in interpreting the experimental trend.