Requirements analysis plays a key role in the software development process. Scenario-based representation is often used for software requirements specification (SRS). Scenarios written in natural language may be ambiguous, and, sometimes, inaccurate. This problem is partially due to the fact that interactions among scenarios are rarely represented explicitly. As scenarios are used as input to subsequent activities of the software development process (SD), it is very important to enable their analysis, especially to detect flaws or problems due to wrong or missing information. This work proposes a Petri-Net based approach as an effective way to analyze the acquired scenarios. To enable the automated analysis, scenarios are translated into equivalent Place/Transition Petri-Nets. Scenarios and their resulting Petri-Nets can be automatically analyzed to evaluate some properties related to correctness, consistency and completeness. The identified problems can be traced back to the scenarios, allowing their revision. We also discuss how correctness, consistency and completeness of scenario-based SRSs can be decomposed in related properties using the NFR approach. Proposal's workability is demonstrated through two running examples.