We present an interprocedural and compositional algorithm for nding pairs of compatible allocation sites, which have the property that no object allocated at one site is live at the same time as any object allocated at the other site. If an allocation site is compatible with itself, it is said to be unitary : at most one object allocated at that site is live at any given point in the execution of the program. We use the results of the analysis to statically preallocate memory space for the objects allocated at unitary sites, thus simplifying the computation of an upper bound on the amount of memory required to execute the program. We also use the analysis to enable objects allocated at several compatible allocation sites to share the same preallocated memory. Our experimental results show that, for our set of Java benchmark programs, 60% of the allocation sites are unitary and can be statically preallocated. Moreover, allowing compatible unitary allocation sites to share the same preallocated memory leads to a 95% reduction in the amount of memory preallocated for these sites.