/o/

Position your tongue at a mid-high level in the back of your mouth, roughly halfway between the high /u/ and mid /ɔ/ positions. Round your lips by bringing the corners together and pushing them slightly forward, almost like you're about to whistle. Your jaw should be moderately open, not too wide.

Important: In American English, pure /o/ almost never exists on its own. It nearly always becomes part of the diphthong /oʊ/, as in words like "go," "know," "boat," or "home." When Americans say these words, the tongue starts at the /o/ position and then glides upward toward /ʊ/. You'll notice your lips round more tightly and your jaw closes slightly as you move through the sound.

If you're seeing /o/ in a transcription, it's often a simplified representation of this /oʊ/ diphthong. The pure monophthong /o/ does appear in some languages like Spanish or Italian, where "no" sounds like a single, steady vowel without any glide.

• Making it too short and pure: Unlike Spanish or Italian, the American "o" sound needs that gliding movement toward /ʊ/
• Insufficient lip rounding: The lips should be noticeably rounded throughout, tightening further at the end
• Skipping the transition: Non-native speakers often produce a quick, steady /o/ without the upward glide, which sounds distinctly foreign to American ears

Practice by saying "oh-oo" slowly, then gradually speed it up until it becomes one smooth gliding motion. Words like "go," "so," "no," and "know" are perfect for practice. Focus on making the sound longer than you might expect: the transition is what makes it sound natural. Record yourself and listen for that characteristic shift at the end.