  We present Chandra observations of black hole X-ray novae V404 Cyg, A0620-00,
GRO J1655-40 and XTE J1550-564 in quiescence. Their quiescent spectra can be
well fitted by a power-law model with slope $\alpha \sim 2$. While a coronal
(Raymond-Smith) model is also a statistically acceptable representation of the
spectra, the best fit temperatures of these models is $\sim 5$ times higher
than that seen in active stellar coronae. These four spectra of quiescent X-ray
novae are all consistent with that expected for accretion via an
advection-dominated accretion flow (ADAF) and inconsistent with that expected
from a stellar corona. This evidence for continued accretion in quiescence
further strengthens the case for the existence of event horizons in black
holes. Both A0620-00 and GRO J1655-40 were fainter than in previous
observations, while V404 Cyg was more luminous and varied by a factor of 2 in a
few ksec. A reanalysis of the X-ray data for XTE J1550-564 shows that (like
V404 Cyg and A0620-00) its luminosity exceeds the maximum prediction of the
coronal model by a large factor. The 0.3-7 keV luminosity of the four sources
studied ranges from $\sim 10^{30}-10^{33}$ erg/s.
