Working with requirements is a knowledge-intensive task. Stakeholders need various information, e.g., for understanding or negotiating the requirements. To understand the information needs of stakeholders we conducted two case studies and interviewed 6 stakeholders. We identified 26 unique information needs, which we represented as questions asked by stakeholders such as 'Are there redundant requirements?' or 'How did other stakeholders prioritize the requirements'. We grouped the needs into five situations in which they were encountered. These were defining, understanding, evaluating, negotiating, and planning requirements. We then surveyed 307 practitioners to quantify the frequencies of these needs and assess how well current tools satisfy them. About 60% of the respondents confirmed that they frequently encounter the needs while their tool support was poor or absent. Requirements engineers and experienced stakeholders were particularly unsatisfied with their tools. The largest gap between the importance of the information and the degree of tool support could be detected for information about the opinions of other stakeholders and conflicting preferences while understanding and negotiating requirements.