American English Phonetics

12.3.4 Syllable Addition

The schwa-glide that is inserted by pre-l breaking in words like rule creates a monosyllabic vowel sequence that is phonetically very similar to the disyllabic sequence that occurs in words like cruel: [ruːᵊɫ] versus [kɹ̥uːəɫ]. Indeed, in the pronunciation of many GA speakers the inserted [ə] may become syllabic through syllable addition, especially after close free vowels and diphthongs. Further examples of such unexpected rhymes are:

rule [ˈruːəɫ]                  cruel [ˈkɹ̥uːəɫ]

mule [ˈmjuːəɫ]              fuel [ˈfjuːəɫ]

foul [ˈfaʊəɫ]                  vowel [ˈvaʊəɫ]

tile [ˈtaɪəɫ]                    dial [ˈd̥aɪəɫ]

oil [ˈɔɪəɫ]                      royal [ˈrɔɪəɫ]

fail [ˈfeɪəɫ]                    portrayal [pʰɔrˈt̠ɹ̥eɪəɫ]

stole [ˈstoʊəɫ]              bestowal [b̥ɪˈstoʊəɫ]

In all of the above examples, glide insertion may apply, especially in the words on the right. The result will be [ˈruːwəɫ, ˈkɹ̥uːwəɫ, ˈtʰaɪjəl], etc.