Capital gains taxes are conjectured to explain upward sloping supply curves in tender offers. This paper analyzes expiration day returns in Dutch auction tender offers to examine this conjecture. A proxy measure for the capital gains of the marginal tendering stockholder is constructed, based on tender offer size and daily price-volume history for one year. Cross-sectional regressions suggest that the tender price increases with the capital gains of the marginal tenderer, but only for firms with low institutional holdings. This is consistent with capital gains tax effects being relevant only when tax-exempt holdings are low.