In this study, we investigated the effects of various source gases (methane, ethane? ethylene, acetylene, and methane + hydrogen) on the friction and wear performance of diamond-like carbon (DLC films produced from the source gases. Specifically, we described the anomalous nature and fundamental friction and near mechanisms of DLC films derived from gas discharge plasmas with very low to very high hydrogen content. The films were deposited on steel substrates by a plasma-enhanced chemical vapor deposition process at room temperature and the tribological tests were performed in dry nitrogen. The tribological tests revealed a close correlation between the source gas chemistry and the friction and wear coefficients of the DLC films. Specifically, films grown in source gases with higher hydrogen-to-carbon ratios had much lower friction coefficients and wear rates than did films derived from source gases with lower hydrogen-to-carbon ratios. The lowest friction coefficient (0.002) was achieved with a him derived from 25% methane +75% hydrogen, whereas a coefficient of 0.15 was seen in films derived from acetylene. Similar correlations were observed for wear rates. Films derived from hydrogen-rich plasmas had the least wear, whereas films derived from pure acetylene suffered the highest wear. We used a combination of scanning and transmission electron microscopy and Raman spectroscopy to characterize the structural chemistry of the resultant DLC films. 2000 Elsevier Science S.A. All rights reserved.