Zagros Airlines, Abadan, Iran, founded 2006.               -  #1,                    #2,             #4:

Zambia Airways, Lusaka, 1967-1994.    -  #3:

ZAS Airline of Egypt (Zarkani Air Service), Cairo, 1981-1995.    -    #1:

Zest Airways, Pasay City, Philippines, founded 2008 by renaming from Asian Spirit 1995-2008 (q.v.).,
merged 2013 with Air Asia Philippines to Air Asia Zest.        -    #5,      #2a:

ZIP,  Calgary,  Canada, 2002 - 2004.    -    #1:

ZIP AIR Tokyo,  Narita, Japan, founded 2018/2020.   -   #1:

ZOOM Airlines, Ottawa, Canada, 2002-2008.   -  #1: