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.

Read more about Om on Last.fm.