We develop the Probability Scaling Method, which rescales short-window announcement period returns; and the Intervention Method, which uses returns associated with intervening events, to estimate value improvements from tender offers. These methods address biases in conventional techniques,
which measure only a fraction of the total tender offer gain; and which include revelation about bidder stand-alone value. Perceived value improvements
are much larger than traditional methods indicate, so that we cannot reject the hypothesis that bidders on average pay fair prices for targets. Furthermore, our new methods affect inferences about economic forces in the takeover market. We identify several effects (higher combined bidder-target stock returns for hostile offers, lower for equity offers, and lower for diversifying offers) that reflect differences in revelation about stand-alone value, not gains from combination.