As there is no dedicated diacritic for protrusion in the IPA, the symbol for the close-mid back rounded vowel with an old diacritic for labialization, ⟨  ̫⟩, can be used as an ad hoc symbol ⟨o̫⟩ for the close-mid back protruded vowel.

Another possible transcription is ⟨oʷ⟩ or ⟨ɤʷ⟩ (a close-mid back vowel modified by endolabialization), but this could be misread as a diphthong.

In English, the symbol ⟨o⟩ is typically associated with the vowel in the "goat", but in Received Pronunciation and General American, that vowel is a diphthong whose starting point may be unrounded and more centered than [o].

Because back rounded vowels are assumed to have protrusion, and few descriptions cover the distinction, some of the following may actually have compression.

The spread-lip diacritic ⟨  ͍⟩ may also be used with a rounded vowel letter ⟨o͍⟩ as an ad hoc symbol, but 'spread' technically means unrounded.