We study how auction design shapes surplus division among bidders. We introduce a parsimonious ex post equity notion and examine standard multi-unit auctions. The equity-optimal pricing depends sharply on the private-common value composition. Among mixed-price auctions, at one extreme, uniform pricing is always optimal for pure common values and, at the other, pay-as-bid pricing is preferred for pure private values under standard regularity assumptions. For any fixed monotone allocation rule, we characterize a BNIC interim-IR implementation that equalizes surplus ex post across all bidders and is revenue-maximizing among those that equalize surplus ex ante; efficient allocation permits parity among winners.

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