It is not uncommon to read in speech studies that subjects were instructed to produce speech samples at a ’’comfortable effort level.’’ In many cases the experiments have made the assumption that this level of effort is more or less constant over repeated occurrences. The purpose of this study was to test the constancy of comfortable effort level in speakers’ utterances across experimental sessions. Sixteen speakers were recorded on each of five successive days while producing a series of vowels and phrases. The only instruction to the speakers was to repeat the utterances at a comfortable effort level. Measures of speaking fundamental frequency (SFF) and vocal intensity (SPL) were obtained from the recordings. Results indicate that variability in both SFF and SPL occurred in the utterances; in many cases (especially for SPL) this variability was considerable. These results suggest that experiments desiring constant vocal productions must be more specific in providing instructions to subjects since comfortable effort level can not be assumed to be constant from one experimental session to the next (especially from day to day).Subject Classification: [43]70.40, [43]70.20.