  This paper presents the fourth extension to the Very Long Baseline Array
(VLBA) Calibrator Survey, containing 258 new sources not previously observed
with very long baseline interferometry (VLBI). This survey, based on three 24
hour VLBA observing sessions, fills remaining areas on the sky above
declination -40 degrees where the calibrator density is less than one source
within a 4 degree radius disk at any given direction. The share of these area
was reduced from 4.6% to 1.9%. Source positions were derived from astrometric
analysis of group delays determined at 2.3 and 8.6 GHz frequency bands using
the Calc/Solve software package. The VCS4 catalogue of source positions, plots
of correlated flux density versus projected baseline length, contour plots and
fits files of naturally weighted CLEAN images, as well as calibrated visibility
function files are available on the Web at http://gemini.gsfc.nasa.gov/vcs4 .
