This article aims to delimit which matters are susceptible of arbitration in disputes with public entities, considering the Brazilian legal system. At the outset, the criteria proposed by the literature, for the interpretation of the legal parameter, are critically analyzed. Then, a formula is proposed to operationalize the one that seems most appropriate. At this point, it addresses the powers of the arbitrators to appraise previous inarbitrable questions necessary for the composition of the patrimonial and disposable conflicts submitted to them by the parties.