A method applied to transactional systems that allows more than one user to access the same record at one time. OCC assumes that multiple transactions can frequently complete without interfering with each other. While running, transactions use data resources without acquiring locks on those resources. Before committing, each transaction verifies that no other transaction has modified the data it has read. If the check reveals conflicting modifications, the transaction attempting to commit rolls back and must be restarted. OCC is generally used in environments with low data contention, which leads to higher overall throughput than other concurrency control methods.