Methanogens/Archaea may be dominant microbes in reduced environments, and methanogenesis can be a component of anaerobic bioremediation. If Archaea are not controlled, then in situ remedial actions employing conventional (i.e., no active control of Archaea) amendments such as [emulsified] oils/lecithins, lactates/sugars, simple hydrogen release compounds, conventional/original ISCR reagents, etc. can generate excessive amounts of methane (CH4) during the reduction of carbon dioxide (CO2). Methane can also be associated with deep earth deposits of crude oil, acquired crude oil in leaking tanks and pipelines or the degradation of petroleum carbon and subsequent reduction of CO2 that is respired during petroleum degradation. The origin of CH4 is not always clear.