A software transactional memory system is provided with multiple global version counters. The system assigns an affinity to one of the global version counters for each thread that executes transactions. Each thread maintains a local copy of the global version counters for use in validating read accesses of transactions. Each thread uses a corresponding affinitized global version counter to store version numbers of write accesses of executed transactions. The system adaptively changes the affinities of threads when data conflict or global version counter conflict is detected between threads.