Analytical models of object lifetimes are appealing because they would enable mathematical analysis or fast simulation of the memory management behavior of programs. In this paper, we investigate models for object-oriented programs such as Java and Smalltalk. We present analytical models and compare them with observed lifetimes for 58 Smalltalk and Java programs. We find that observed lifetime distributions do not match previously proposed object lifetime models, but do agree in salient shape characteristics with the gamma distribution family used in statistical survival analysis for general populations.