The invention provides a method for generating droplets. Extremely fine droplets may be generated (on the order of 1 picoliter or less) using focused acoustic energy to eject the droplets from a reservoir containing two or more immiscible fluids. The droplets may include immiscible fluids or a single fluid. Typically, the droplets are ejected onto discrete sites on a substrate surface so as to form an array thereon. In some instances, the reservoirs contain layers of immiscible fluids, wherein an upper layer exhibits a nonuniform thickness. In such a case, fluid from a lower fluid layer may be propelled through an aperture region of the upper layer.