This article aims to trace the hitherto little-known controversy involving Maurice Allais, François Divisia, Harold Hotelling, and Gérard Debreu in the immediate postwar years. The controversy turned on “dead loss,” a measure of the maximum value of available surplus serving as a gauge of economic efficiency and social welfare. The protagonists argued about how it should be expressed mathematically, the hypothesis underpinning it, and its general significance. The paper draws heavily on unpublished materials (letters and notes) to unfold the different stages of the dead loss controversy and shows that it was driven by an intricate interlacing of technical advances in welfare economics with Allais's personal ambition to spearhead the revival of French economics. Eventually, this controversy (and the tense exchange between Allais and Debreu that came with it) proved a remarkable—although tacit—driving force behind Debreu's contributions of the early 1950s.