They still sell sustained energy, but like ericm979 says above, perpetuem is a more current product. As a longer distance ride fuel it works pretty well. The biggest downside is that the protein in it starts to sour after a few hours (especially when its hot out). One serving provides about an hour's worth of calories(at least about as many as your stomach wall can pass in an hour, not as many as you can burn). I tend to put two servings in a bottle and use it in conjunction with other calories sources (hammer gels/cliff bars/Hammer Heed/real food) on rides over about 4 hours. It seems to work pretty well and doesn't upset my stomach. Hammer sells a "long ride" fueling sampler pack if I recall correctly if you want to try both perpetuem and sustained energy out. I've had nothing but good dealings with them for a few orders so far.