The first series of commercially successful descarga jam sessions were recorded mostly between 1956 and 1958 at the Panart studios in Havana. The Panart descarga sessions were released in three volumes under the title "Cuban Jam Session"; they would sell over a million copies. Volumes I (1956, yellow cover) and II (1957, blue cover) were recorded under the direction of Julio Gutiérrez with Peruchín on piano. The sessions were recorded by engineer Fernando Blanco in Havana and then sent for editing to New York. According to the original liner notes of Volume I, the studio doors were opened at 10:30 pm and the recordings took place throughout the night. The jams in Volume I revolve around canción, mambo, chachachá and conga themes; the longest track, "Opus for Dancing", lasts 10 minutes. Volume II kicks off with "Descarga caliente", a 17-minute montuno jam recorded in 1952 and thus considered the first recorded descarga, while side B includes three jams recorded later: rumba, chachachá and batá (Santería-based). Volume III (1958, red cover) was directed by "tresero" Niño Rivera and it comprises three montuno tracks combined with swing, guajira and chachachá, plus a guaguancó-comparsa. The only musicians to participate in all three sessions were Alejandro "El Negro" Vivar (trumpet), Emilio Peñalver (tenor saxophone) and Salvador "Bol" Vivar (double bass). Another session entitled "Cuban Jam Session with Fajardo" took place under the direction of flautist José Fajardo in 1957, but only four tracks could be recorded. The album was finished in Miami in 1964. It was the first descarga album in the charanga format and it features jazz-inspired mambos, chachachás, guajiras and montunos.