  We present results on the effects of interstitial oxygen and carbon on a
bulk-niobium superconducting radio-frequency cavity. Previous experiments have
shown that high-temperature (~800 $^\circ\text{C}$) nitrogen-doping plays the
dominant role in the reduction of the electron mean free path in the RF
penetration layer of niobium that leads to a decrease in microwave surface
resistance and a suppression the temperature-dependent component of the surface
resistance with increasing accelerating gradient. In this work, we show that
oxygen and carbon-doping has very similar effects on cavity performance,
demonstrating that these effects are not unique to nitrogen. The preparation
method used in the introduction of interstitial oxygen and carbon has the
advantage that it is done at lower temperatures than that of high-temperature
nitrogen-doping and does not require post-treatment electro-polishing.
