Darek Oleszkiewicz (born February 20, 1963), also known as Darek Oles, is a jazz bassist, composer, arranger, and educator.

Oleszkiewicz was born in Wrocław, Poland, on February 20, 1963. He lived in Kraków in the early 1980s, then moved to Los Angeles in 1987 or 1988 and attended California Institute of the Arts from 1989 on a full scholarship. While studying at Cal Arts he was a protégé of Charlie Haden. In the early 1990s and 2000s he built a reputation on the West Coast of the United States. He co-founded the Los Angeles Jazz Quartet in 1993, with saxophonist Chuck Manning, guitarist Larry Koonse, and drummer Kevin Tullius. They recorded for Naxos Records and Not Two Records.

Oleszkiewicz's first album as sole leader was Like a Dream, which consisted largely of his own compositions. It included quartet and trio tracks, and duets with pianist Brad Mehldau. He had earlier played on Mehldau's Largo. Oleszkiewicz was featured prominently with Koonse on the 2006 album Storybook.

In 2010 Oleszkiewicz was a co-leader with Peter Erskine, Bob Mintzer, and Alan Pasqua on the album Standards 2: Movie Music. Oleszkiewicz was co-leader with Adam Czerwniński for the album Raindance.

Oleszkiewicz is a faculty member at California Institute of the Arts, and the University of Southern California, He continues to record, including on trombonist Bob McChesney's Chez Sez in 2015, and with other USC faculty members, including on Kait Dunton's Mountain Suite in the same year. He was part of the Peter Erskine Trio that was nominated for the 2022 Best Jazz Instrumental Album Grammy Award for Live in Italy.

On his debut as leader, Oleszkiewicz's style was described as containing "the inevitable lineage to Scott LaFaro and Bill Evans, [...and] combines a certain economy of style that is reminiscent of Charlie Haden". The woodiness of his tone was also compared with Haden's, with the addition of "a certain Gary Peacock-like edge to it".

With Peter Erskine and Alan Pasqua

With Peter Erskine, George Garzone and Alan Pasqua