Subtle variations in voice (phonatory) quality may reveal aspects of the speaker's mood and attitude, and are thus an important aspect of speaking style. This paper illustrates current research being carried out by the authors on the voice source correlates of a range of such quality differences. The voice qualities looked at include modal, breathy, whispery, tense, lax and creaky voice, following the description of Laver (1980) and analyses presented here focus on a word extracted from a propose passage read with these qualities. The principal method used for analysing the voice source involved inverse filtering of the speech wave. In order to quantify the source characteristics, a four parameter voice source model (the LF-model) was matched to the inverse filtered waveform. Frequency domain analyses of the speech waveform, based on narrow band spectral sections and on spectral averaging, were also carried out. Detailed comparisons of the data measured directly from the glottal waveform and those measured from the speech output yield insights which could not be inferred from either alone. Results suggest a number of important differences between the qualities as well as considerable dynamic variation within a single quality. The data should also prove useful for resynthesis, which is an important tool for testing perceptual aspects of voice quality; e.g., the attitudinal and emotional colouring that may be associated with particular voice qualities.