Rate constants and branching ratios have been measured for the reaction of O-2(+) with CH4 over the temperature range from 500 to 1400 K. The rate constants increase dramatically over this temperature range, in good agreement with a previous study from our laboratory. A complex chemistry was found. The main product at low temperature, CH2O2H+, disappears almost completely at high temperature, in part due to thermal dissociation. The main products at high temperature are CH4+ and HCO+; the latter ion has not been observed previously. Also prominent at high temperature are H3O+ and CH3+. A small amount of CH3O+ is observed at all temperatures. H2O+ is observed in small quantities at high temperature. Branching ratios for the reaction of O-2(+) with CD4 are also reported, confirming the ion assignments. Comparison to drift tube and beam results indicates that vibrational excitation of the CH4 promotes several of these channels more than other forms of energy. Channels which proceed through the t-CH3OOH+ (2)A(') intermediate (described in the accompanying paper) are probably not strongly dependent on the form of energy, although uncertainties prevent a definitive conclusion. The charge-transfer channel and the channels requiring substantial rearrangement are greatly enhanced by vibrational excitation. Thus, specific channels do appear to be governed by vibrational excitation.