Coatings suitable for use as protective oxide-forming coatings on Nb-based substrates exposed to high temperatures and oxidative environments. The coatings contain chromium and/or molybdenum, preferably contains silicon, and optionally contains niobium, titanium, hafnium, iron, rhenium, tantalum, and/or tungsten, which in combination form multiple intermetallic phases, which in combination form one or more intermetallic phases that promote the formation of a slow-growing oxide scale. Depending on the particular coating composition, the intermetallic phases may be: a silicon-modified Cr2Nb Laves phase and optionally a chromium solid solution phase, a CrNbSi intermetallic phase, and/or an M3Si intermetallic phase where M is niobium, titanium, and/or chromium; or M5Si3, MSi2 and/or M3Si2 where M is molybdenum, niobium, titanium, chromium, hafnium, iron, rhenium, tantalum, and/or tungsten.