This study investigates whether rhythm metrics can be used to capture the rhythmic differences between spontaneous and read English speech. Transcription of spontaneous speech tokens extracted from a corpus is read by three English native speakers to generate the corresponding read speech tokens. Two data sets are compared in terms of seven rhythm measures that are suggested by previous studies. Results show that there is a significant difference in the values of vowel-based metrics (VarcoV and nPVI-V) between spontaneous and read speech. This manifests a greater variability in vocalic intervals in spontaneous speech than in read speech. The current study is especially meaningful as it demonstrates a way in which speech styles can be differentiated and parameterized in numerical terms.