The /ɔ/ vowel is usually spelled <or>, <our>, and <oar>, but we also see <al> in hall, <au>, <aw> and <ar> after <w> in warship. The /3/ vowel is spelled <er>, <ir>, <ur>, <ear>, and <or> after <w> in worship.
This is a contrast between two long vowels. They are fairly close together in the mouth but are distinguished by lip-rounding. They can sometimes be a source of confusion, but are not a problem for any particular group of learners.
Interesting pairs include:
The density figure is fairly high at 7.62%. The set makes 120 semantic contrasts giving a loading of 51.5%.
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Credit: John Higgins