A software transactional memory system is provided that creates an array of transactional locks for each array object that is accessed by transactions. The system divides the array object into non-overlapping portions and associates each portion with a different transactional lock. The system acquires transactional locks for transactions that access corresponding portions of the array object. By doing so, different portions of the array object can be accessed by different transactions concurrently. The system may use a shared shadow or undo copy for accesses to the array object.