Existing nativized loanword studies have traditionally suggested that there are three epenthetic vowels in Japanese, which reflect both phonotactic restrictions and articulatory properties of certain consonant-vowel sequences in the language. Recent findings, however, call this tri-partite epenthesis pattern into question: First, several studies suggest that this epenthesis pattern is not true in the realm of perception and is not completely regular in production, and second, the relevant phonotactic restrictions seem to be weakening even outside of epenthesis contexts. This paper therefore investigates the extent to which the spontaneous choice of epenthetic vowels in the production of Japanese conforms to the traditional tri-partite pattern. Epenthesis was induced by presenting pseudo-word stimuli of the form of [aCCa] (C = a voiced consonant) to subjects orthographically. The findings suggest that indeed, the production pattern does not fully conform to what is generally reported for nativized loanwords; in particular, the traditionally “default” vowel [ɯ] is used by our participants frequently in all contexts, including the two where [o] or [i] is usually reported. That said, we also show that there is considerable variability across speakers as to which vowel is epenthesized, especially in the palatal context, and this variability includes tokens of vowels similar to all possible lexical vowels of Japanese.