This article reports on an exploratory study that investigated the comparability of listening assessment tasks used to assess and report learning outcomes of adult ESL learners in Australia. The study focused on the effects of task characteristics and task conditions on learners” performance in competency-based listening assessment tasks that require learners to demonstrate specific listening behaviours. Key variables investigated included the nature of the input and the response mode. Quantitative and qualitative analyses of test scores suggest that speech rate and item format influence task and item difficulty. However, the complexity of the interaction between text, item and response makes it difficult to isolate the effects of specific variables. Implications of these findings for assessment task validity and reliability are considered and practical consequences for assessment task design in outcomes-based systems are discussed.