It is widely known that the volumes of limit orders and market orders display
non-trivial statistical properties. For example, the sizes of volumes can take
on many different values across several orders of magnitude, with a marked
preference for whole numbers like 5, 10, 100. These studies have been centered
on the volume of incoming orders or of realized transactions. In the present
work we analyze the statistical properties of volumes stored at the best ask
and best bid. We measured both dynamical properties as well as properties that
do not directly depend on time. Of the properties found some are also present
in the time series of price returns while others turn out to be particularly
idiosyncratic and distinguish the stochastic nature of volume time series from
that of price returns time series