Under the CDM rules, emission reduction activities are categorised into four classes called "measures". A project activity can include single or multiple measures. There are currently four types of measures covered in the CDM guidelines:

(i)    Fuel and/or feedstock switch (example: switch from naphtha to natural gas, or switch from limestone to gypsum in cement clinker production)

(ii)   Switch of technology with or without change of energy source (example: energy efficiency improvements, power generation based on renewable energy);

(iii)  GHG destruction (example: landfill flaring, incineration of HFC23 gas vented from HCFC22 production unit);

(iv)  GHG formation avoidance (example: use of biomass that would have been left to decay in a solid waste disposal site resulting in the formation and emission of methane, for energy generation). (EB 69, Annex 21, paragraph 9)