The adsorption at 90 K of hydrogen, carbon monoxide, and benzene on Ni-n/O-0.5/W(110) (with n = 1-10) has been studied by thermal desorption, x-ray photoemission spectroscopy, ultraviolet photoemission spectroscopy, low-energy electron diffraction, and work function measurements. The surfaces are relatively inert to hydrogen adsorption, with estimated quasisaturation uptake being H/W = 0.18 for n = 1 and increasing to 0.36 for n = 10. In contrast, CO and C6H6 adsorb readily on Ni-1/O-0.5/W(110), with saturation coverages of CO/W = 0.85 +/- 0.09 and C6H6/W = 0.18 +/- 0.03, respectively. These values are comparable to coverages obtainable on clean W(110), namely, CO/W = 0.70 and C6H6/W = 0.18. Coadsorption of Ni and O on W(110) and subsequent annealing to 500-1000 K leads to segregation of Ni and 0, with the formation of Ni crystallites largely [111] oriented along the surface normal. The heights of these Ni "towers" can be adjusted by varying the amounts of coadsorbed oxygen and Ni. The Ni crystallites resist sintering, even when annealed at 1000 K for 3600s. Adsorption of H-2 and CO on them at 90 K was also investigated, and found to be less than expected from the estimated overall Ni surface area.