Research on online discourse has found that computer-mediated communication (CMC) such as e-mail and text-chat exhibit features of both speech and writing (Danet & Herring, 2007). Such differences reflect the influence of contextual, social and technological factors on language practices (Androutsopoulos, 2006). A prominent contextual factor found in the computer-enhanced language classroom is the type of task learners engage in using CMC. Research on L2 performance within the complexity-accuracy-fluency (CAF) framework has found that task characteristics and task conditions exert a systematic influence on learners’ linguistic choices (Skehan, 2001). Accordingly, this study uses exploratory corpus-based techniques to compare the spoken and written features found in L2 learner text-chat output produced under two task conditions: on-task and off-task text-chat. The chatscripts analyzed in the present study were generated during text-chat interactions produced by 30 adult high intermediate and advanced Swedish university learners of English paired with US English speakers. Pairs met online for two 20 minute sessions to completed two collaborative writing tasks. After completing the task, participants used any remaining time to continue chatting. On-task chat was operationalized as chat turns bounded by task opening (e.g. Shall we begin?) and task closing sequences (e.g. That was all of my words.). Off-task chat was operationalized as chat turns preceding task opening sequences and chat turns following task closing sequences. Chatscripts were split to separate ‘on-task interaction’ from ‘off-task interaction’, in order to obtain two corpora representative of the language produced in these different conditions. On-task and off-task interaction were compared using the corpus-based techniques key-word analysis (Scott 1997) and concordancing. Analysis revealed intriguing differences in the relative use of features related to speech (e.g. first and second person pronouns, inserts) and writing (e.g. subordinators, stance adverbs) in the two task conditions.