This work investigates how vowel duration and vowel quality affect degrees of vowel-to-vowel coarticulation. The effects of these two factors on vowel-to-vowel coarticulation have previously received little study. Phonological durational differences due to vowel length distinction were examined in Thai. It was hypothesized that shorter vowel duration could result in more vowel-to-vowel coarticulation, and further that the vowel /a/ would allow more vowel-to-vowel coarticulation than /i/ or /u/ cross-linguistically. Thus, the susceptibility of different vowel qualities to vowel-to-vowel coarticulation was examined using Thai data. Results show that shorter vowel duration did not affect vowel-to-vowel coarticulation; and the lower the vowel, the more susceptible it is to coarticulation. Possible factors contributing to such patterns are discussed.