||The present paper has as goal the analysis of the urban sprawl phenomenon, from a planetary scale, assuming the hypothesis that this is an unsustainable process. It aims to demonstrate that what were initially a way of human settlement characteristic of many civilizations (northern and eastern Europe, nomadic tribes of America and Africa, etc.) and that represented in the early twentieth century a vernacular urbanism design, has become, particularly in the 70ís of the last century, an International Style, a general trend in global scale. A model as a result of the widespread American Dream, based on the extensive land consumption, the car as basic transportation, and oil as primal energy, and some authors have characterized as counter-urbanization (Berry) desurbanization (Berg), edge-cities (Garreau) metapolis (Asher) or diffuse city (Indovina). Despite the diversity of urban development, the increasing consumption of land, the excessive use of land as a scarce resource, it is a constant in the urbanization process in the early twenty-first century around the world. For this purpose the paper analyses in a first step, the urban sprawl in ten selected metropolitan areas: New York, Los Angeles, Chicago, Mexico, Sao Paulo, Tokio, Shangai, Moscow, London, Madrid and Barcelona. The first specific objective is to delimitate, measure and understand the urban continuum inside and outside the administrative boundaries. The morphological analysis of conurbation will serve to identify the core city from the surrounding countryside and to compare the different structures of the studied megacities. The comparison between the different models of urbanization of the selected megacities allows making a first approach of the differences and similarities of these megacities on the phenomenon of urban sprawl and the interaction existing between land consumption and a number of urban sustainability indicators, such as mobility, energy consumption and the generation of CO2. In parallel, the degree of monocentrism or polycentrism of the study areas will be analyzed, in order to validate the hypothesis relating to the improved environmental performance of polycentric metropolitan systems over those characterized by the macrocephaly of a single center.