Phonetic mergers in American English have been studied throughout the last half century. Previous research has contributed social and phonetic explanations to the understanding of front and back vowel mergers before /l/, front vowel mergers before nasals and phonetically unconditioned back vowel mergers. Using data from the Linguistic Atlas of the Gulf States (LAGS) and the Linguistic Atlas of the Middle and South Atlantic States (LAMSAS), this thesis examines the spread of the front vowel mergers in Mary and merry and the back vowel mergers in horse and hoarse. The two complementary sources of data allow for a social and phonetic approach to the examination of the merger.