Service delivery platforms in telecommunication environments aim to host multiple services and to provide context-awareness and personalization features. This calls for an appropriate management of user profiles containing general user information as well as situation-dependent user preferences for the contextual personalization of these services. We present a user profile selection approach that decides on the selection of matching situation-dependent user preferences concerning the user's current situation. The presented approach takes advantage of ontology reasoning and is compared to other approaches. The comparison shows that our ontology reasoning based approach allows for more expressiveness concerning the specification of situation-dependent user preferences and hence leads to an added value for platform users.