This study investigates the production of vowels in unstressed syllables by advanced German learners of English in comparison with native speakers of Standard Southern British English. Two acoustic properties were measured: duration and formant structure. The results indicate that duration of unstressed vowels is similar in the two groups, though there is some variation depending on the phonetic context. In terms of formant structure, learners produce slightly higher F1 and considerably lower F2, the difference in F2 being statistically significant for each learner. Formant values varied as a function of context and orthographic representation of the vowel.