A carbon tax was introduced in 2014 for fossil fuel production. The base rate is USD 3.5/tCO2 and offsets are allowed through CERs from CDM registered projects. It is not a tax on the full carbon content of fuels, but rather on the additional amount of emissions that would be generated if the fossil fuel were used instead of natural gas. Natural gas is entirely exempted from the tax (SEMARNAT, 2014).