The results of a three-dimensional ocean experiment in Acoustic Tomography (AT) are, at this time, being processed and reviewed by the originators in the University Consortium [W. Munk and C. Wunsch, Deep-Sea Res. 26A, 123–161 (1979)]. The hope is that AT will some day soon provide an economical and accurate means to monitor changes in the sound velocity structure over large expanses of the ocean volume. NOAA is attempting to anticipate the engineering implications of operating and maintaining basin-wide and smaller-scale AT systems. We are concerned with the likely bounds on performance and, ultimately, will study the relationships between performance and benefits in the civilian sector—in particular, for climate and fishery studies. Estimates of the sound speed distribution are made by inverting travel time relationships. The accuracy and resolution of these estimates can themselves be estimated and, when combined with field data, used to study the performance of a given AT system versus given design parameters. In our present work, these performance relationships are studied and interpreted by means of a well-known approach of geophysics, the Backus-Gilbert theory. In this approach, the estimate is interpreted as a weighted local average of the unknown function, with statistical error. An averaging kernel is defined which, when integrated with the actual unknown function, produces a local average; this kernel can, therefore, be interpreted as a property of the system. The width of this function defines resolution length. A trade-off relation exists between accuracy and resolution length. Examples will be presented for a two-dimensional problem, a tomographic configuration in a horizontal ocean slice.