The /ʊə/ diphthong ranks eighteenth in frequency among the English vowels, which partly accounts for the shortness of this list.
39 of the 40 pairs are monosyllables. Spellings of /i/ include <ee>, <ea>, the letter names B, D, P and T, the musical note names mi and ti, Spellings of /ʊə/ are <oor>, <ure>, and <our>, together with the exceptional <ewe> and <ue> in crewel/cruel.
There might be some dispute over the <lure> spelling, as to whether there is palatalisation and whether that would render these pairs non-minimal. Note the partial homograph tours, plural of tour, and Tours, the French city with an anglicised vowel sound.
The mean density value is 1%. The 40 pairs make 31 semantic contrasts, giving a high loading of 78%.
alee allure B boor B's boors be boor bean bourne beans bournes bee boor bees boors been bourne creel crewel creels crewels creel cruel D dour lea lure leas lures lead lured lee lure lees lures me moor mead moored meed moored mi moor P poor pea poor pee poor she sure T tour T's tours T Tours tea tour tea Tours teas tours tease tours tee tour teed toured tees tours tee Tours ti tour ti Tours ye you're
John Higgins, Shaftesbury, January 2011.