Reaction of 197Au atoms with CO has been studied in inert hydrocarbon matrices in a rotating cryostat at 77 K by EPR, FTIR, and UV/visible spectroscopy. Au(CO)2 has been positively identified by FTIR spectroscopy and there is evidence for the formation of AuCO, a gold microcrystallite – CO complex and, upon annealing, Au2(CO)4. Electron paramagnetic resonance spectra are consistent with the formation of Au(CO) (OC) with the magnetic parameters: a13 = 325 MHz, a17 = 44 MHz, and g = 2.0014 and a gold microcrystallite – CO complex with g = 2.014. An intense broad absorption in the optical spectrum at 525 nm is assigned to Au(CO)2 and a less intense narrow band at 320 nm is assigned to AunCO. There is no spectroscopic evidence for the formation of Au(CO)3 in hydrocarbon matrices. Keywords: gold carbonyls, EPR, FTIR, UV/visible, matrix isolation.