Oscars

Well I would say that 100 gallon would work tank mates convicts firemouths white tipped columbians anything bigger than an oscars mouth

100g would be fine, two Oscars work together well sometimes and sometimes they don't. More often than not two will get along in a decent sized tank. Occasionally you will get an Oscar that just doesn't like another oscar in the tank.
As far as tank mates, Pleco's, pictus cats, firemouths, dempseys, cons, larger gourami's, so on and so forth. Any heavy bodied fish that gets 4 inches or larger and has a strong personality will be fine. Thinner bodied fish will need to be 6-7 inches if kept with adult Oscars. With a 100g IME you will want to limit it to about 4 or 5 fish depending on how large the other fish are. a 100g looks really big until the oscars grow up and then it looks really small even if it is enough tank for the fish. Right now when I look at my 115g with the Oscar being the largest of 5 fish it looks like I should get a larger tank.

As far as their personality, tank raised Oscars generally are very friendly and could be equated to an aquatic puppy dog.

Although you will see oscars at 16 inches on rare occasions, those fish were usually fed specifically for rapid growth. Genetics also have a big play in fish size. Most Oscars top out below 14". I don't feed for growth, my Oscars generally hit the 9 inch mark in the first year, and then slowly fill out and grow from that point for the rest of their lives. It is not difficult to limit food without compromising health of the fish. Meaty diets and heavy feeding will enhance growth. Lots of staple food and limited feeding will give you healthy fish that do not grow quite as rapidly.

In other words be prepared for the possibility of a 14-16 inch fish but don't be suprised if they end up at a healthy 12 inches.
dave

A 100gal would be bordering on minimal IMHO, much better for two Adult O's would be a 125-150gal. For large cichlids and such always get the largest possible tank you can afford and accomodate.
A 100gal would suit a single O very well and even allow for a tankmate(s), any tankmates would need to be large enough not to fit in a O's mouth and able to defend themselves.
A medium sized Pleco or Cat can be a good tankmate.
The compatibilty of potential tankmates will rest soley on the individual personality/temperament of your O.
O's do not need tankmates and will do just fine as a solitary fish as long as you give'em attention.

I've sent you a PM regarding a source of Oscar specific info, please read thru the 'Articles Section' for detailed info on keeping O's.