Nozick’s ‘utility monster’ is often regarded as impossible, because one life cannot be better than a large number of other lives. Against that view, I propose a purely marginalist account of utility monster defining the monster by a higher sensitivity of well-being to resources (instead of a larger total well-being), and I introduce the concept of collective utility monster to account for resource predation by a group. Since longevity strengthens the sensitivity of well-being to resources, large groups of long-lived persons (...) may, if their longevity advantage is sufficiently strong, fall under the concept of collective utility monster, against moral intuition. (shrink)