A number of investment cases in the aftermath of the Argentine economic crisis 2001/2002 have addressed important issues of state of necessity. The tribunals affirmed that the codification of this defence in the 2001 ILC Articles on State Responsibility largely reflects customary international law and they rejected the argument that the highly complex nature of necessity characterized it as a non-justiciable political question. ICSID and other tribunals have also concurred on some crucial aspects of the necessity defence, like the potential qualification of economic emergencies as necessity situations or the fact that necessity can be invoked only in extreme cases. Nevertheless, the application of these principles to the actual situation in Argentina led to divergent and partly conflicting outcomes. After assessing the relationship between derogation clauses contained in many investment treaties and state of necessity this contribution focuses on specific aspects which entitle a State to invoke necessity as a ground for not fulfilling its obligations. It pleads for a proportionality approach in determining whether the actual measures adopted should be regarded as the only means to safeguard State interests. Similarly, it supports a nuanced assessment concerning the contribution element by requiring that it be substantial.