The genus Oncidium (Onc) contains 600 species from throughout Central America and South America. They grow in a wide variety of environments. If you know a little about where the species grows, they do very well in cultivation.
Oncidium sphacelatum grows from Mexico south to Venezuela in low altitude rain forest. It is warm to hot growing, but does very well intermediate. It is giant sized and grows long, pendulous spikes of 6 feet or more.
As far as culture goes, this is considered a beginner plant but not a good indoor plant because of the plant size and the length of the flower spike. Having said that, I don't get good results with Oncidiums in either greenhouse.
This is potted in bark in a 4-inch plastic pot. It has four pseudobulbs and one new growth and stands 14 inches above the pot. The newest pseudobulb is the largest but the plant is still quite small for this species.