Bulk and bulge most often are pronounced with the vowel [uh] of buck. In South Midland and Southern U.S. the [oo] of book and bull commonly occurs among all speakers. Standard British speech has only [uh]. Both types exist in British regional speech, and both were brought to the colonies, where each came to predominate in a different area and was carried west by migration.
“Bulk” and “Bulge” Pronunciations