Collaborative Software Engineering (CSE) is a rapidly growing field. Tools such as IDEs are now beginning to incorporate new collaborative features. We have developed several real-time CSE tools which support fine-grained collaboration. In this paper we present an empirical evaluation to investigate the potential benefits of our tools for collaborative source code development. Our results show that for the two typical types of collaborative programming scenarios studied, users of CSE tools achieve task completion rates at least twice as fast as those obtained from their single-user counterparts. Additionally, participants indicated strong support for the concept of CSE tools. These results encourage us to continue developing our CSE tools, and to investigate their use in other software engineering contexts.