According to Ordo Templi Orientis’ U.S. Grand Lodge website: “Aleister Crowley wrote Liber XV in 1913 in Moscow, the year after his appointment by Theodor Reuss as the X° Head of the British Section of O.T.O. According to W. B. Crow in A History of Magic, Witchcraft and Occultism (Aquarian Press, London 1968), Crowley wrote it “under the influence of the Liturgy of St. Basil of the Russian Church.” Crowley published the Gnostic Mass three times during his life: in 1918 in The International, in 1919 in The Equinox, Volume III, No. 1 (the “Blue Equinox”), and in 1929 in Appendix VI of Magick in Theory and Practice. Theodor Reuss published a German variant in 1918. It was first publicly celebrated on Sunday, March 19, 1933 e.v. by Wilfred T. Smith and Regina Kahl in Hollywood, California.”
You can find the current version of the Coptic Liturgy of St. Basil here: http://www.coptic.net/prayers/StBasilLiturgy.html
You can listen to recordings of Crowley intoning the first four “Collects” from the Mass.