We investigate in a spatial Cournot competition setting how much product research and development (R&D) investment firms make in order to differentiate their goods. The model features a location competition in the first stage, R&D competition in the second stage, and Cournot competition in the third stage. There are two differentiation methods in the model-spatial differentiation affecting the firm costs, and differentiation in the demand function affecting the demand levels. We find that comparing to the setting with no spatial connotation, the firms tend to invest less in product R&D. We also consider welfare implications. Although the firms employ maximum differentiation in equilibrium, there are cases in which welfare can be improved if the firms are to locate closer to each other.