This article, as its title suggests, wishes to discuss some methodological issues of historical research on the industrial past of gas lighting and its sources. I focus more on the example of the gas factory of Athens, a challenging, though not unique, example where the researcher is called upon to document the past of an industry or a productive activity, without the safety of collected documents or a complete corporate record of this activity. I use the term Ground Zero to denote this contradiction of the absence of historical records: I describe by this term the moment when a researcher has to examine a historical economic phenomenon without a certain amount of data. Gas companies operated thanks to an urban pipe network that extended inside the boundaries of a city. Most gas companies took over public lighting, and from 1890 onwards the supply of energy (lighting, heating, appliances) to residences and offices. From my archival investigation, it emerged that the gas lighting plants of some cities belonged to the local government and others to private individuals. The documentation of the historical route of this energy and its establishments in Greece was a challenging task. I deem that the mapping of this route will prove useful to future researchers.