Some traditional Mexican open-air markets called "tianguis", such as the Mercado Margarita Maza de Juárez in Oaxaca, are separated into a wet market ("zona húmeda") and a dry market ("zona seca"). A 2002 study observed a trend that Mexican consumers, especially those in the middle class, increasingly prefer supermarkets for beef purchases as opposed to traditional wet markets. In 2014, a study of Mexican beef retail also noted an ongoing transition from traditional full-service wet markets to self-service meat display cases in supermarkets.