In a generational garbage collector, a decision is made to pre-tenure, or allocate new objects directly in the old generation, by a two step process. In the first step, during a young-generation collection, the number of bytes that survive collection is determined for each allocation site and a predetermined number of sites with the highest number of surviving bytes are selected as candidate sites. In the second step, during a subsequent young-generation collection, the survival rates are determined for the candidate sites and objects to be allocated from sites with a sufficiently high survival rate are allocated directly in older generations.