Program HYPOERR evaluates the performance of a small network of arbitrary seismic arrays in determining coordinates and times of seismic events. A linearized inversion following the method of Uhrhammer (1980) is performed for a layered velocity structure by determining the eigenvalues and eigenvectors of the partial derivatives of travel time for P and/or S phases with respect to hypocenter position and origin time for each station in the array. A series of covariance matrices is then obtained to evaluate statistical errors for a specified grid of hypocenter locations at any given depth. Contour plots can then be made of the matrix elements by using standard contouring software. Examples are given for (1) the case of a hypothetical quadrapartite array and (2) and actual eight-station ocean-bottom seismometer array deployed around the 95.5 W. Galapagos propagating-rift zone.