Aside from his teaching duties, Darek has been very active as a performer and became one of the most sought after bass players on the West Coast. "Oles" (his American nick-name) had the opportunity to perform and record with the greatest masters in jazz. A partial list of his collaborations include: Brad Mehldau, Billy Higgins, Pat Metheny, Joe Lovano, Eddie Henderson, Charles Lloyd, John Abercrombie, Bennie Maupin, Lee Konitz, Peter Erskine, Alan Pasqua, Bennie Wallace, Victor Lewis, Harvey Mason, Dave Grusin, Art Farmer, Horace Silver, Alice Coltrane, Ravi Coltrane, James Newton, Arthur Blythe, Lew Tabackin, Steve Kuhn, Gary Smulyan, Ronnie Cuber, Billy Hart, Kevin Hays, Munyungo Jackon, Steve Hass, Toshiko Akiyoshi, Marian McPartland, Janis Siegel, Bob Brookmeyer, Curtis Fuller, Roy McCurdy, Tom Harrell, Larry Goldings, Bill Stewart, Chris Potter, Kei Akagi, Billy Childs, Bob Sheppard, Joe LaBarbera, Bill Cunliffe, Patrice Rushen, Bennie Golson, Piotr Baron, Teri Lynn Carrington, Buddy De Franco, Terry Gibbs, Anthony Wilson Nonet and Los Angeles Jazz Quartet.
With these and many others artists Darek has recorded approximately 100 albums and performed hundreds of concerts throughout America, Europe and Asia. Several of those recordings were nominated for Grammy Awards.
In 2003, Darek was also nominated to Fryderyk's Awards in Poland in the category "Jazz Musician Of The Year".
Darek's first recording project as a leader "Like A Dream" with Brad Mehldau and Bennie Maupin was released by Cryptogramophone Records in 2004 and gained a critical acclaim worldwide. In 2005 Darek "Oles" Oleszkiewicz was voted the "Best Accoustic Bassist" in the Jazz Top readers poll in Jazz Forum European Magazine.