The walking speed of a human is approximately 2.9 kilometers per hour. At a normal walking speed, bipedal humans are more energy efficient than knuckle-walking chimpanzees and normal quadrupedal animals of the same time. If we measure energy cost in terms of milliliters of oxygen per gram per kilometer and compare humans with chimpanzees, we get the following cost relationships:
When this is compared to a normal quadrupedal animals of roughly the same size as a human (say a small gazelle), one finds that the energy cost comparably favors bipedality (measures are in percent difference from the quadruped.)