This category contains operas which are specified in their libretto as having only one act. However, the number of acts is not necessarily an indication of the length of the opera. While most one-act operas have a relatively short running time (under 90 minutes), this is not always the case. For example, the one-act opera Das Rheingold has an approximate running time of 2 hours, 35 minutes, while Puccini's four-act opera La bohème and Monteverdi's five-act opera L'Orfeo both have running times of approximately 2 hours. Leoncavallo's two-act opera Pagliacci has a running time of just over an hour, while Richard Strauss' one-act opera Salome has a running time of nearly two hours.


All running times are taken from: The Earl of Harwood and Antony Peattie (editors), The New Kobbé's Opera Book, 11th Edition, 1997, New York: G.P. Putnam's and Sons.