The paper discusses studies undertaken to identify the cause(s) for differential settlements experienced by a large floating roof tank. The studies included an evaluation of existing subsurface and tank performance data, additional subsurface exploration and laboratory test programs, a monitoring program during the restricted use of the tank and recommended remedial measures to allow full use of the tank. It is concluded that the affected portion of the tank was sited over a thicker and more compressible soil layer than the remaining portions and that releveling by mudjacking would allow unrestricted future use of the tank