The weak-field version of optimal control theory is applied to the design of laser pulses to achieve control over product formation. Computations on the optimal control of the two-photon dissociation of Na-2, yielding the products Na(3s)+Na(3p) and Na(3s)+Na(4s), are described. The optimization is performed by maximizing either the difference between, or the ratio of, the probabilities of producing a product in these two channels. The dependence of the quality of control on the potential surfaces involved is also investigated as is the strategy through which optimized control is achieved.