Reporting the results of an instrumental acoustic examination of the vowel systems of ten Jamaican Creole (or basilect-) dominant and nine Jamaican English (or acrolect-) dominant speakers, this article links phonetic features with sociolinguistic factors. The nature and relative role of vowel quantity and quality differences in phonemic contrast are considered. The question of whether contrastive length operates in speakers' phonological systems is addressed by comparison of spectral and temporal features. Intraspeaker variation in vowel quality is found to play an important role in stylistic variation, demonstrating the complexity of variation in Jamaican varieties. The complex vowel quality (spectral) and quantity (temporal) relations reported here extend our understanding of the spectral and temporal characteristics of vowels involved in phonological contrasts in Jamaican varieties, the range of phonetic variation to be found within a postcreole continuum, and the interaction of phonetic factors in the expression of stylistic variation.