Since the 1860s, petroleum companies, through their influence on local governments, port authorities, international actors and the general public gradually became more dominant in shaping the urban form of ports and cities. Under their development and pressure, the relationships between industrial and urban areas in port cities hosting oil facilities evolved in time. The borders limiting industrial and housing territories have continuously changed with industrial places moving progressively away from urban areas. Such a changing dynamic influenced the permeability of these (...) borders. Port cities are nodes and logistic points where various flows of commodities, wealth, and knowledge gathered before further re‐distribution. These flows affected port cities by changing their spatial organization and the availabiity of space between borders. The main question here is: How did industrial and urban borders evolve through time in port cities? Through a historical analysis, the article explores the settlements of oil facilities and the influence of oil companies over local, regional, and national governments in creating borders and how it influenced the porosity of port cities. This article, through the petroleum narrative, illustrates the impacts of past borders on the contemporary urban form through the evolution of the French port city of Dunkirk, in the North of France. As a historical study, the article analyzes the changing relationships between petroleum industrial sites and housing areas in the city of Dunkirk, using aerial pictures, archival sources, and regulations of different periods. The importance of this analysis lies in knowing that former oil sites previously located on the periphery of Dunkirk, that were forgotten by the authorities are now located within the current urban tissue. This process demonstrates the importance of historical developments to understand current challenges in the urban planning of industrial port cities. (shrink)