Carbon neutral fuels are those that neither contribute to nor reduce the amount of carbon into the atmosphere. Before an agency can certify an organization or individual as carbon neutral, it is important to specify whether indirect emissions are included in the Carbon Footprint calculation. Most Voluntary Carbon neutral certifiers such as Standard Carbon in the US, require both direct and indirect sources to be reduced and offset. As an example, for an organization to be certified carbon neutral by Standard Carbon, it must offset all direct and indirect emissions from travel by 1 lb CO2e per passenger mile, and all non-electricity direct emissions 100%. Indirect electrical purchases must be equalized either with offsets, or renewable energy purchase. This standard differs slightly from the widely used World Resource Institute and may be easier to calculate and apply.