Low viscosity, radiation curable fluid formulations that can be used advantageously as radiation curable, inks. The formulations are easily prepared for use in ink jet systems. The viscosity of the compositions is low enough so that conventional solvent is not required in order to satisfy the requisite low ink jet viscosity specifications. After curing, the compositions form durable, weatherable, abrasion resistant, printed images on a wide variety of porous and nonporous substrates. The formulations are very suitable for outdoor printing applications, especially for printing outdoor graphics onto a variety of surfaces, including vinyl or other polymer films commonly used for signage, retroreflective signage or other retroreflective items.