The present invention is directed to a catalyst system for synthesizing rubbery polymers, such as polybutadiene rubber and styrene-butadiene rubber, having a high trans microstructure. The catalyst system, in one embodiment, includes (a) a barium salt of an alcohol that is soluble in a hydrocarbon solvent, and (b) an organomagnesium compound. In one example, the alcohol is a primary or secondary alcohol. The catalyst system can further optionally include an alkali metal alkoxide, an organolithium compound, an amine compound, or mixtures thereof.