This paper presents the sixth extension to the Very Long Baseline Array
(VLBA) Calibrator Survey. It contains the positions and maps of 264 sources 
of which 169 were not previously observed with very long baseline 
interferometry (VLBI). This survey, based on two 24 hour VLBA observing 
sessions, was focused on 1) improving positions of 95 sources from previous 
VLBA Calibrator surveys that were observed either with very large a priori 
position errors or were observed not long enough to get reliable positions 
and 2) observing the remaining new flat-spectrum sources with predicted 
correlated flux density in the range 100--200 mJy that were not observed 
in previous surveys. Source positions were derived from astrometric analysis 
of group delays determined at the 2.3 and 8.6 GHz frequency bands using the 
Calc/Solve software package. The VCS6 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://vlbi.gsfc.nasa.gov/vcs6.