There are multiple artists with this name:
1) OM is a duo from San Francisco, California, United States, formed in 2003 by the rhythm section of the stoner metal band Sleep. The band's first three albums feature Al Cisneros on vocals and bass and Chris Hakius on drums.
The band's music is similar in structure to Tibetan and Byzantine chant and is rich in rhythm and melody. Their music and lyrics lift off at the beginning and slowly mutate giving a feeling of evolution inside each song. The vocals have a monotone quality, producing, on some tracks, a noticeable hypnotic effect of the sort that tends to be appealing to the devotees of the many various genres of druggishly-bent, "space" music - but which not all music calling itself stoner rock necessarily is able to cause.
On January 2008, Hakius left the band and was replaced by drummer Emil Amos, of Grails. OM have since released Gebel Barkal, a 7" for Sub Pop's Singles Club, a live vinyl-only LP titled Conference Live on Important Records, and on September 2009 their fourth full-length studio album God is Good was released by Drag City.
On May 2011 Drag City confirmed on their website that the band was working on a new album, titled “Advaitic Songs”, which was released in June of 2012 and met with critical acclaim.
Al Cisneros - bass guitar, vocals
Emil Amos - drums
Robert Aiki Aubrey Lowe - vocals, keyboards, percussion, tambura (2011-present)
2) OM was a jazz rock band signed on the German ECM label in the 1970s. Formed in Lucerne, Switzerland, in 1972 and named after Coltrane's darkly convulsive album, the members of OM were initially inspired as much by the rock of Jimi Hendrix as by the new developments taking place in improvisation. "Electric jazz - free music" was their rallying cry, and they played it loudly. All in their early 20s when the group was launched, the members of OM achieved an early success at the Montreux Festival in 1974 which helped to put them on the map, and brought them to the attention of ECM.
Four albums were recorded for ECM's sister label Japo, between 1975 and 1980: Kirikuki; Rautionaha; Om with Dom um Ramao; and Cerberus. In jazz rock's heyday, OM was one of the few bands who were approaching jazz from a rock direction, rather than vice versa: most of fusion's traffic took the opposite route. The validity of their approach is borne out by this compilation, with material chosen by the band.
After OM broke up in 1982, its members continued to appear intermittently on ECM recordings, in combinations with each other and separately. Guitarist Doran, drummer Studer and bassist Burri all appeared on the album Musik für Zwei Kontrabässe, Elektrische Gitarre und Schlagzeug. Doran and Studer were also part of the power trio Red Twist and Tuned Arrow, and Studer was also in Pierre Favre's Singing Drums collective, and Rainer Brüninghaus's Continuum band with Markus Stockhausen. Saxophonist Urs Leimgruber has been away from ECM the longest - but also in his case there are some enduring connections: Urs today fronts a trio with bassist Barre Phillips and pianist Jacques Demierre, and plays regularly with Marilyn Crispell. He has become a major voice on the free improvisation scene. Indeed, all OM members have made their mark.
3) OM is the first Bulgarian ethno ambient band, formed by founder Nikolay Ivanov in 1991. The purpose is the creation of cross culture synthetic and plastic music, which is aiming to associate elements from the ethnic music, ambient, jazz, new age, and minimalism. Nikolai Ivanov realized his conviction about the synthesis of East and West ideas and the global "ethnologisation" of contemporary art. OM uses instruments and motives taken from the Balkan tradition: tambura, tarambuka, bagpipe, instruments from the East-sitar, tabla, ghatam, sas, specific Tibetian singing mixed with acoustic guitar, forte piano, bass and electronic instruments, programming and samples.
The group offers a lot of concerts and in many occasions takes part in most of the Bulgarian festivals: Saloon of the Arts; Apolonia; Varna Summer; August in Art; Sofia Jazz Peak; Music Jam; jazz festivals in the country and in Sofia. The musicians are aspiring to a maximum "opening" - they play in clubs with electronic ambience, in jazz and fusion clubs, ethno clubs and they make acoustic concerts and vanguard performances. OM and Nikolai Ivanov have made artistic tours in France, Germany, Hungary, Spain, Norway, Croatia, Poland, Austria, Turkey, India, Nepal, and China. On May 1996 OM together with musicians realized the highest concert in the world- at 5345 metres at Kalapatar (under Everest), which was registered in the files of Guinness. OM takes part as well in lots representative activities, like: concert Milenium (on invitation of the President of Republic) - author Nikolai Ivanov, concert at EXPO 2000 - Hanover, concert at the Congress center in New Delhi, etc. http://www.myspace.com/424438162
5) OM was a jazz rock band from Barcelona, Spain, formed in 1969. They released a self-titled album in 1971. Led by superb Catalan guitarist Jordi Toti Soler after his previous band Pic-Nic split, were one of the most interesting outfits to ever come out from Barcelona. Starting in 1968, their first recordings were done as a backing group for other artists like folk-singer Maria del Mar Bonet or american hippie Joe Skladzien, but most notably Pau Riba whom they backed on his debut LP the legendary Dioptria, one of the finest pieces of European psych ever. During all their early work, the band benefited from the organ playing of one of the most talented catalan pianists, Jordi Sabatés (of Ocells del més enllà fame) as well as the musical talents of two English brothers: drummer Peter Hodgkinson and his brother Tim on sax and keys (this is, of course, the same Tim Hodgkinson who founded Henry Cow, together with Fred Frith).
By the time they released their LP on Edigsa in 1971, Om was already an experienced band, with important studio work on their back and countless gigs, having backed American blues-man Taj Mahal in his Madrid 1969 concerts. One particularity of Om was that, rather than having an established line-up, they worked as a musical concept where it was not so important the individuals playing as it was the resulting sound. Their only LP shows how, through the works of Miles Davies, Gary Burton and John McLaughlin, they had developed their sound from its original psych/folk-rock beginnings to an intensely psychedelic jazz rock fussion. A classic album that is hardly known outside Spain and ranks amongst the best of the era, sharing shoulders with similar underground European experiments by Min Bul, Colhemec Ensemble, Xhol, Dharma Quintet, Sunbirds, Full Moon Ensemble or the more progressive output of the British jazz of the era: John Surmans Trio, Nucleus or Michael Gibbs. Strictly limited to 500 copies. High quality gatefold sleeves reproducing the beautiful Tony Cepuka's original psychedelic artwork from 1971's first press on Edigsa. Insert with liner notes by Wah Wah's Marc Argenter and Fermi Puig. Includes also repro of big Om poster (coming originally with the first copies of the LP). Bonus 7" single reproducing Om's single with non-LP tracks 'Vindrà La Llum' / 'Waiting For Godot' (actually the only one released under their own name and not as a backing band).
6) OM is an experimental rock band from Palermo, Italy, formed in 2002.