  The 5n-vector ensemble method is a multiple test for the targeted search of
continuous gravitational waves from an ensemble of known pulsars. This method
can improve the detection probability combining the results from individually
undetectable pulsars if few signals are near the detection threshold. In this
paper, we apply the 5n-vector ensemble method to the O3 data set from the LIGO
and Virgo detectors considering an ensemble of 201 known pulsars. We find no
evidence for a signal from the ensemble and set a 95% credible upper limit on
the mean ellipticity assuming a common exponential distribution for the
pulsars' ellipticities. Using two independent hierarchical Bayesian procedures,
we find upper limits of $1.2 \times 10^{-9}$ and $2.5 \times 10^{-9}$ on the
mean ellipticity for the 201 analyzed pulsars.
