This paper considers Bayesian revenue maximization in the $k$-unit setting . Four basicmechanisms among others have been widely employed in practice and widelystudied in the literature . We investigate the largest possible ratio between the two revenues (a.k.a.\ the revenue gap), overall possible value distributions of the buyers . Within one group, the involved two mechanisms have an asymptoticallytight revenue gap of $1 + \Theta(1 / \sqrt{k)$. In contrast, any twomechanisms from the different groups have an tight revenue gapof $\Theta(\log k)$1 = 1 + 1 /\sqrt {k) The anonymous mechanism group,

Author(s) : Yaonan Jin, Shunhua Jiang, Pinyan Lu, Hengjie Zhang