Oxygen-incorporated hydrogenated amorphous carbon films were grown by the integrated distributed electron cyclotron resonance plasma technique from a mixture of acetylene and oxygen. It has been found that the increase of the oxygen to acetylene gas ratio results in more oxygen incorporation up to O/(O+C)=0.2 with a decrease in the hydrogen concentration within the film as measured by the nuclear reaction analysis (NRA) and a combination of the elastic recoil detection analysis and Rutherford backscattering techniques. The spectroscopic ellipsometry in the range of 1.5–5 eV showed a negligible decrease of the E04 optical band gap for increasing the oxygen content. At the same time, the decrease of the refractive index from 2.2 to 2.0 denotes the decrease of the films density, which was independently estimated by NRA. The visible (488 nm) Raman spectroscopy showed that the increase of the oxygen content favors the clustering of the six-fold sp2C rings. The Fourier transform infrared spectroscopy gives evidence of both C–O and CO bonding configurations. No evidence of O–H bonds formation is found. Simultaneously, the chemisorption of CO2 seems to increased with increasing the oxygen to acetylene gas ratio, which is consistent with the lower film density. The previously trends denote the “softening” of the films, which is consistent with the significant decrease (of about 35%) of the compressive stress allowing the growth of thicker but still transparent films.