This paper reports the results of an experiment on the effects of six speaking styles on some of the acoustic properties of speech. The experiment was part of an exploration of within-speaker variation in connection with automatic speaker verification (ASV), pursuing the hypothesis that the elicitation of style variation in the training phase of an ASV system (‘structured training’) would enhance the performance of the system. Swedish-speaking subjects produced a digit sequence at varying speaking rates and loudness levels, and also with simulated denasality (pinched nose) and under cognitive stress. Duration of vowels and consonants, and formant frequencies of vowels, were measured. A number of consistent patterns of variation emerged for duration and vowel quality and are reported here. The discussion explores the relation between the patterns observed and the success, or in the case of speech under stress the failure, of structured training in reducing the error rates in ASV.