Pressure sensitive adhesive (PSA) compositions that include at least one urethane (meth)acrylate oligomer having a molecular weight between about 2,000 g/mol and about 50,000 g/mol and an OH number of from 0.01 mg KOH/g to 100 mg KOH/g, at least one mono (meth)acrylate functional monomer and at least one tackifying resin. The PSA systems may also optionally include other additives, such as at least one initiator system that includes at least one photo-initiator or free radical initiator. The PSA systems are liquid at a temperature of 25° C.±2° C. with a viscosity of 15,000 cPs or less and are adapted to form smooth, uniform coatings or films upon curing without the application of heat, whereby the resulting films have advantageous properties with respect to peel strength, tack and shear resistance. In embodiments, the PSA systems include less than 1 wt % of solvent and less than 1 wt % of water or are free of solvent and are free of water.