OxyElite has 1,3-dimethyhlamylamine which is a VERY strong stimulant, with effects on the brain not terribly far from a light cocktail of ephedrine and methamphetamine, it is also the major ingredient in UPSLabs other hit product, Jack3d. Jack3d has made this stimulant very popular and a number of brand included it in their preworkout and stimulant mixes, but it was recentely slated for potential banning by the FDA, and 20 major manufacturers including UPSLabs were served warnings to prepare to stop selling it. While this substance does aid in burning fat, more than anything its just a stimulant and in my opinion should be avoided in a thermogenic formula unless your taking it with the intention of a speed based pre workout/thermogenic combination.
The other major ingredients, that trigger bodyheat and fat burning are Bacopa Monniere and Bauhinia purpea, both of which riase your bodys thyroxine (T4) and triiodothyronine (T3) thyroid hormone levels, which serve the function of regulating your bodies metablism, rate of protien synthasis, glycogen breakdown, triglyceride breakdown etc -- all things which *might* be desired for a fat burning orientated supplement, especially if working out hard with it.
It is worth noting 1,3-dimethylamylamine is banned by several athletic organizations, so do tread with consideration if you compete at a tested level.