Civil law systems commonly espouse a concept of 'financial equilibrium' in contracting, which may be established in general administrative law, or defined in more detail in the PPP context in PPP-specific law or a particular contract. Financial equilibrium provisions entitle an operator to changes in the key financial terms of the contract to compensate for certain types of exogenous event that may otherwise impact returns. Adjustments are based on a mutually agreed financial model that is maintained over the lifetime of the contract. Three causes of unexpected changes that merit financial equilibrium are typically defined as Force Majeure (major natural disasters or civil disturbances), factum principis (government action) and ius variandi (unforeseen changes in economic conditions). The PPP in Infrastructure Resource Center Website [#286] provides more information and references on financial equilibrium clauses in its section on 'Key Features of Common Law or Civil Law Systems'.