Free On Demand?

I was curious, is the Premium On Demand free or not? We just got Uverse, so we have pretty much every channel for a low rate for a year. We've been watching Boardwalk Empire on the HBO premium page, and I'm just making sure it is free. I assume it is, because on other items, like newer movies, there is a price, but no price shows up on the separate Boardwalk Empire episodes.