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Hello, I have 2 tiger Oscars, one bigger then the other, but close in size. The larger Oscar drives the smaller one into the far corner of the tank  ( 55 gal ) Ive had the larger Oscar for 2 years now and the smaller one for just about 1 year. When come feeding time, they seem to get along,no fighting. They beat each other up on a daily basis, diff times during the day i hear a loud slam,which is the large Oscar chasing the smaller one. The smaller Oscar from time 2 time gets scrapes and marks on her or him.Also the smaller Oscar seems discolored,not as colorful as the larger fish. Looks like the a shirt that has been washed to many times,faded,dusty color. What can I do to help them get along, rearranging the tank works for 5 min then the war is back on 

Well, I can tell you a few things, but Oscars are not totally predictable.  The obvious guess is that you probably have two males, and territory is an issue.  Even if they're a male and a female it could still be a territory issue.  55 gallons is a bit on the small side for two Oscars.  Can work if they get along, but it's tight, and for young fish feeling their oats, it just isn't a lot of space.  You can try things like:

Rearrange the tank, using decorations to break up the sight lines and suggest "two territories.  Maybe it'll work.  My bet is that it won't.

Put in a divider.  A strong one will keep the violence down, but you may not be satisfied with the result.

Get a bigger tank.  A 55 is marginal for 2 Oscars.  75 is better.  I'd recommend going to a 5' or 6' tank -- say a 125.  Square footage is more importand to cichlids than water volume.  I believe that you'll see significant relaxation of hostilities with a 6 foot tank.  With these fish, it'll also be easier to keep the water quality high.  No guarantees of course.  Oscars tend to decide whom they like and dislike regardless of our views and theories.  Good luck, and let us know...

My 2 Oscars fought really bad when I had them in my 55 gallon tank. Constantly. They grew up together but when they got big they just went at each other all the time. It got to the point where I had to buy a bigger tank or they would have killed each other.

I moved them into a 150 gallon tank. They still fight once in awhile, when one of them goes on the others side (they have chosen sides of the tank). But it has gotten much better. They can actually live happily in the same tank.

I would get a much bigger tank, and see if it helps. If not, then they aren't going to be able to live together.

I would def. look into getting a bigger tank. One oscar is fine for a 55 gal. that is what mine is in now but with 2 in there, they may feel uncomfortable or crowded. So that might help out a little. Usually 2 males fight like that when there is a different size. If you have had one for a while and then bring another in, the one you have had may feel like he has to defend his territory. I would just try a bigger tank that way they have more space to stay apart as well to grow. If that can't be afforded then try a divider. I haven't heard anything bad about dividers but you probably wanted your fish to be together. Sorry i can't help more.