NRG Ensemble was an American free jazz ensemble founded in the late 1970s by saxophonist/multi-instrumentalist Hal Russell.The group's personnel was somewhat fluid, but included a core of drummer Steve Hunt, saxophonist Mars Williams, guitarist/trumpeter Brian Sandstrom, and bassist Kent Kessler. Their music kept free jazz alive in Chicago throughout the 1980s, when it had largely disappeared from the jazz landscape. Russell was the primary composer, but the other musicians contributed songs as well. Their punning song and album titles (Conserving NRG) reflected the humor that permeated Russell's music. After Russell's death in 1992, the NRG Ensemble recruited saxophonist Ken Vandermark as a replacement, recording three more albums under the leadership of Williams.