I was researching into tankmates for the Oscar I'm planning on getting, and I saw Black Lancer Catfish on the section here. I looked into these fish (Bagrichthys macracanthus) and saw that you should only keep 1 male with 3-4 females, and that they grow to 6-10", averaging about 8". I was wondering if anyone has had experience keeping Black Lancers with Oscars. 8" makes me wonder if a full size Oscar might look at them as lunch, and I know this can be dangerous, especially with catfish. Also, I was considering a 90 gallon for the one Oscar and 4 or 5 catfish, but I know that many fish would be pushing the max load for a tank that size. Would my fish be ok as long as I took proper care of them or should I get a larger tank? I know that's a lot of questions for my first thread, thanks for any help you all can give.

As long as the fish isn't too small then it'll be okay with the Oscar. I'm not sure how quickly these fish grow. They come from the same part of the world as the clown Loach which grows quite slowly. If this is the case then you might need to find one that is already big enough so as not to become lunch, I would say no smaller than 4 inches. I reckon you be okay with one Oscar and may be three of these catfish in a 90 gallon tank if you have good filtration.

in my fish keeping, i have two reason, finding an alternative source of food;
and love watching fish. for that reason, i don't like fishes that are bottom dweller
or those that are always hiding. having said that, i love to watch oscar, knife fish,
pangasius (ID shark), SD, pacu, aro, and angel fish.

Yeah you should be okay, As long as it is not crowded when it comes to the end of it, it's you're choice, what do you think?

You will be ok as long as they dont fit in the oscars mouth and are prepared to put the work into maintaining the tank