We establish stability, monotonicity, concavity and subadditivity prop
erties for open stochastic storage networks in which the driving proce
ss has stationary increments. A principal example is a stochastic flui
d network in which the external inputs are random but all internal how
s are deterministic. For the general model, the multi-dimensional cont
ent process is tight under the natural stability condition. The multi-
dimensional content process is also stochastically increasing when the
process starts at the origin, implying convergence to a proper limit
under the natural stability condition. In addition, the content proces
s is monotone in its initial conditions. Hence, when any content proce
ss with non-zero initial conditions hits the origin, it couples with t
he content process starting at the origin. However, in general, a tigh
t content process need not hit the origin.