XIAMEN Airlines, Xiamen, China, founded 1984.
-           #8,                            #7(clean white)/#7a(thin recycled paper),                                 #9:

-                        #10,                                                 #11,                                       #12:

-         #15:

Xinhua Airlines, Beijing, China, 1992 - 2007 merged into Grand China Air.  #2:

China Xinjiang Airlines, Urumqi, Xinjiang, 1985-2003 integrated into China Southern.  - #6:
(see more under C/China ....)

XL Airways, Frankfurt, Germany, 2006-2012.   #4     and  #6:

XL Airways France, Paris, founded 2006 by renaming from Star Airlines(q.v.). - #1,  #2,  #3:

XL.com Airways UK, Crawley, UK 2006-2008. 
Founded 1994 as Sabre(q.v.), 2001 renamed as Excel (q.v.), 2006 renamed as XL.com
#2                        and                                    #3: