In some circumstances a generational garbage collector may be made more efficient by “pre-tenuring” objects or directly allocating new objects in an old generation instead of allocating them in the normal fashion in a young generation. A pre-tenuring decision is made by a two step process. In the first step, during a young-generation collection, an execution frequency is determined for each allocation site and sites with the highest execution frequency are selected as candidate sites. In the second step, during a subsequent young-generation collection, the survival rates are determined for the candidate sites. After this, objects allocated from sites with sufficiently high survival rates are allocated directly in the old generation.