Unaffordable housing and inadequate security of tenure in the private rental market are major issues for low-to-middle income households in Sydney. The city has seen an increased competition in the private rental housing market with upward pressure on rents. Shared housing, via online accommodation listings, has emerged as a popular and affordable housing choice for many Sydneysiders. Research aimed at gauging the impact of shared housing, particularly room sharing on occupants and wider-market rental housing is sparse, albeit there is growing evidence of residential overcrowding, upward pressure on rents, gender and ethnicity based discrimination, poor health and safety standards, and limited legal protection for room sharers. Due to the absence of research and longitudinal data about distinct forms and trends of the emerging room sharing, state and local authorities are unable to track the on-going practices and thereupon to regularise the shared housing sector. This paper addresses the questions of the geography and characteristics of room sharing, advertised via online shared accommodation listings, and its impact in terms of residential overcrowding and rental affordability. A mixed method approach was mobilised combining web scraping and the geographic approach. Web scraping was used for online data collection drawing on a popular shared accommodation listings website; www.gumtree.com.au. The geographic approach involved Geographic Information System (GIS) tools for data analysis and mapping. The findings may provide insights for policymakers and development practitioners seeking to address the issues of monitoring and regulation of informal practices of room sharing through online listings in Sydney.