The Lewisham, City Airport and Woolwich Arsenal extensions were designed, financed, built and maintained by private companies (concessionnaires): City Greenwich Lewisham (CGL) Rail, City Airport Rail Enterprises (CARE), and Woolwich Arsenal Rail Enterprises (WARE).
Tre nyere forlængelser, Lewisham, City Airport og Woolwich Arsenal, er også blevet projekteret, finansieret, bygget og nu vedligeholdt af private selskaber: City Greenwich Lewisham (CGL) Rail, City Airport Rail Enterprises (CARE) og Woolwich Arsenal Rail Enterprises (WARE).