This paper studies the design of position auctions when bidders have multi-unit demands for advertising positions. I propose an ascending clock auction with two stages: allocation stage and assignment stage. The allocation stage determines the quantity of positions assigned to each advertiser using a generalized version of the Ausubel (2004) auction under the context of differentiated items. The assignment stage determines the ranking of advertisements using a generalized version of the generalized English auction under the context of multi-unit demands. I show that this two-stage ascending clock auction dynamically implements the VCG outcome in an ex post perfect equilibrium under pure private values.
