An apparatus (2) may have a processing element (4) for performing data access operations to access data from at least one storage device (10, 12, 14). The processing element may have at least one transactional processing resource (10, 18) supporting processing of a transaction in which data accesses are performed speculatively following a transaction start event and for which the speculative results are committed in response to a transaction end event. Monitoring circuitry (30) captures monitoring data indicating a degree of utilization of the transactional processing resource (10, 18) when processing the transaction.