Amorphous hydrogenated oxygenated carbon (a-C:O:H) films were deposited from C6H6/O-2/He/Ar mixtures in a deposition system fed rf power. The principal variable was the percentage of oxygen in the feed, R-OX. Film structure and composition were investigated as a function of R-OX using transmission infrared- and x-ray photoelectron spectroscopy. To some degree, greater values of R-OX lead to greater incorporation of oxygen functionalities such as OH, C-O, and C=O into the deposited material. As revealed by ultraviolet-visible spectrophotometry, the optical gap E-04 increased from similar to 3.1 to similar to 3.5 eV as R-OX was increased from 0% to similar to 50%. Semiempirical methods (PM3 and ZINDO-S/CI) allow modeling of the dependence of E-04 on R-OX. Broad agreement between the results of the experimental and theoretical analyses was obtained.