Gray, H. P. (1973). The balance of payments costs of international travel. Centre D' Etudes du Tourisme.
Citazione stile Chigago Style (17a edizione)Gray, H Peter. The Balance of Payments Costs of International Travel. Aix-En-Provence: Centre D' Etudes du Tourisme, 1973.
Citatione MLA (9a ed.)Gray, H Peter. The Balance of Payments Costs of International Travel. Centre D' Etudes du Tourisme, 1973.
Attenzione: Queste citazioni potrebbero non essere precise al 100%.