Approximately 30 to 50 percent of the total baryons in the present
universe is supposed to take a form of warm/hot intergalactic medium
(WHIM) with $10^5 {\rm K}< T < 10^7 {\rm K}$ which has evaded the
direct detection so far. In order to elucidate the nature of such dark
baryons, we propose a dedicated soft-X-ray satellite mission, {\it
DIOS} (Diffuse Intergalactic Oxygen Surveyor).  We have recently
carried out a set of cosmological hydrodynamic simulations to explore
the science with DIOS. In this talk I describe how one can locate
cosmic dark baryons and estimate their physical and statistical
properties via their emission and absorption signatures.