AbstractTomographic velocity estimation of a three‐dimensional (3D) anomaly as a function of time is implemented by the simultaneous iterative reconstruction technique (SIRT) using synthetic observed travel times as data. Rays are retraced every 6–7 iterations to ansure consistency between rays and velocities. An expanding steam front modeled within a shallow reservoir is imaged at two points in time using three different survey geometries containing both cross‐well and well‐to‐surface paths. Synthetic data can be used to evaluate and optimize survey design and resolution prior to field data acquisition. Resolution is evaluated by computing point spread functions and can (theoretically) be made as high as desired (up to the limit imposed by wave phenomena and the noise in the data) by increasing the number of independent observations and correspondingly reducing the image voxel size. ©1994 John Wile