Pressure data from well tests and interference tests contain information about the distribution of permeability and porosity within the reservoir, but the relationship between the data and the rock properties is quite complex. Estimates of permeability and porosity are easily obtained through standard applications of inverse theory methods, yet the relationship of the estimates to the true values is usually not clear. In this paper I discuss the concept of ＇＇resolution of the model,＇＇ the idea that the estimate at any location is influenced by the rock properties at neighboring locations and, sometimes, by rock properties at quite distant locations. If the estimation process is very good, the estimate is influenced only by rock properties near the estimation point and the spread of the resolution is said to be small. I use this measure to compare the value of interference tests with standard well tests for estimating permeability and porosity in the interwell region. In general, adding a third well test is more effective than adding an interference test to estimate permeability. Porosity is more difficult to resolve, but interference tests are generally more effective than well tests at improving the resolution of the estimate.