The possible sources of hydrogen contamination of Diamond-Like Carbon (DLC) films deposited using Unbalanced Magnetron (UBM) sputtering of carbon from a graphite target have been studied. Without deliberate introduction of hydrogen or hydrocarbon gas, magnetron sputtered DLC can contain significant amounts of hydrogen, from 4 to 23 %, by changing the base pressure (or residual gas pressure, rgp) of the deposition system from 3 × 10−6 to 4 × 10−5 Torr. This hydrogen contamination contributes to a large change in the optical band gap (0.2 to 1.0 eV) and lowers the density of the films. The hydrogen content in the films comes from water vapor in the deposition system, mainly absorbed in the graphite target, which is dissociated and/or ionized in the plasma. Hydrogen gas has been introduced up to a pressure of 7 × 10−1 Torr at a base pressure of˜1 × 10−1 Torr in order to simulate high residual gas pressure conditions. The properties of the plasma and the films produced at high base pressures have been compared to those at a high partial pressure of hydrogen gas. For the plasma properties, the electron temperature, T e , and the ion density, n i , were measured by using a double Langmuir probe. The films were characterized by using Ultraviolet-Visible, Rutherford Backscattering/Elastic Recoil, and X-ray Photoelectron Spectroscopies (UV-VIS, RBS/ERS, and XPS).