[1] He moved to New York City and played with Mal Hallett, Joe Venuti, Smith Ballew, Mike Durso (1933–34), Phil Harris (1935–39), Gene Krupa (1939–40), and Bob Crosby (1940–42).
[1] In 1943, he relocated to Los Angeles and played with Eddie Miller, Bunk Johnson, Shorty Sherock, Jack Teagarden, and Wingy Manone.
[1] In 1948, he moved back to Chicago and there worked with Bud Freeman, Art Hodes and Danny Alvin.
[1] O'Brien had recorded with Freeman as early as 1928; other recordings include with Eddie Condon (1933 and later), Fats Waller, Mezz Mezzrow, George Wettling (1940), Charles LaVere (1944), Albert Nicholas (1959), and Smokey Stover.
[1] His lone session as a bandleader yielded two singles for Jump Records in 1945, which were also released under LaVere's name.