In current project environments, requirements often evolve throughout the project and are worked on by stakeholders in large and distributed teams. Such teams often use online tools such as mailing lists, bug tracking systems or online discussion forums to communicate, clarify or coordinate work on requirements. In this kind of environment, the expected evolution from initial idea, through clarification, to a stable requirement, often stagnates. When project managers are not aware of underlying problems, development may proceed before requirements are fully understood and stabilized, leading to numerous implementation issues and often resulting in the need for early redesign and modification. In this paper, we present an approach to analyzing online requirements communication and a method for the detection and classification of clarification events in requirement discussions. We used our approach to analyze online requirements communication in the IBM® Rational Team Concert® (RTC) project and identified a set of six clarification patterns. Since a predominant amount of clarifications through the lifetime of a requirement is often indicative of problematic requirements, our approach lends support to project managers to assess, in real-time, the state of discussions around a requirement and promptly react to requirements problems.