ive got two oscar in my 55gallon tank... an albino and the other one is a tiger (no idea about their sexes)... ive seen them lip locking few days ago... ive been observing them since and found out that everytime i feed them both my albino is showing off his/her gills when both are close together... is this still a sign of mating ritual??

Okay, 55 gallons is really only big enough for one Oscar. How big are the Oscars at the moment? Lip locking and flaring of the gills isn't an indication that you have a breeding pair. It could just be plain old aggression. A breeding pair will perform these types of behavior but you will only know for sure after you see them laying eggs.

Like I said, your tank really isn't big enough for two Oscars, if this is indeed aggression, the lack of space could make matters even worse as time goes on

albino is at least 7 inches long and my tiger is about 8... not sure about their ages but im sure albino is older than tiger by a month or 2...