  We present a comprehensive analysis of a particular class of coronal mass
ejection (CME) event, called streamer-blowout CME (SBOs). The events are
characterized by a gradual swelling of the overlying streamer, lasting hours to
days, followed by a slow, wide CME, generally exhibiting a 3-part structure,
which leaves the streamer significantly depleted in its wake. We identify 909
SBO events in the LASCO/C2 observations between 1996 and 2015. The average
blowout lasts for 40.5 hours but the evacuation can take days for some events.
SBO-CMEs are wider and more massive than the average CME. Their properties
generally vary during and between solar cycles. Their minimum (maximum) monthly
occurrence rate of one (six) events in cycle 23 has doubled in cycle 24---a
probable manifestation of the weaker global fields in the current cycle. The
locations of SBOs follow the tilt of the global dipole (but not from 2014
onwards), do not correlate with sunspot numbers and exhibit flux rope
morphology at a much higher rate (61%) than regular CMEs (40%). We propose that
these characteristics are consistent with SBOs arising from extended polarity
inversion lines outside active regions (e.g. quiet sun and polar crown
filaments) through the release, via reconnection, of magnetic energy, likely
accumulated via differential rotation.
