This article describes a successful 4-D seismic pilot project in Duri Field, Indonesia, the site of the world’s largest steamflood. Two baseline and six monitor 3-D seismic surveys were recorded over the same steam injection pattern between 1992 and 1995. Seismic analysis, thermal simulation, and acoustic modeling show the engineering relevance of these data and provide new insights into the seismic response of reservoirs during active steamflooding. Analyses of the data demonstrate that, for the Duri steamflood, the horizontal and vertical distribution of steam can be tracked over time.