A homemade pendent drop/bubble tensiometer is applied to perform the surface/ interfacial tension measurements for the binary water + ethylene glycol monoisobutyl ether (iso-C4E1) mixture over the temperature range from 25 to 150 degrees C and over the pressure range up to 100 bar. The symbol CiEj is the abbreviation of a nonionic polyoxyethylene alcohol CiH2i+1(OCH2CH2)(j)OH. The wetting behavior of the iso-C4E1-rich phase at the surface of the aqueous phase is systematically examined according to the wetting coefficient determined from the experimental results of surface/ interfacial tensions. It is found that the iso-C4E1-rich phase exhibits a sequence of wetting transitions, nonwetting --> partial wetting --> complete wetting, at the water surface in the water + iso-C4E1 system along with increasing temperature. On the other hand, the iso- C4E1-rich phase undergoes a wetting transition from partial wetting to nonwetting at the surface of the aqueous phase by increasing the system pressure at a fixed temperature near the lower critical solution temperature (LCST) of the closed-loop miscibility gap in the water + iso- C4E1 system.