In addition to the issues stated in the previous page, the following completeness issues should also be considered:

• Companies in the oil and natural gas industry often burn unprocessed or partially processed natural gas for fuel (i.e., non-marketable fuel). The consumption of these fuels may not be accounted for in sectoral consumption statistics. For instance, consumption of non-marketable gas is much less likely to be actually metered and may have substantially different carbon factors and calorific values than marketable gas due to greater concentrations of impurities and heavier-than-methane hydrocarbons.
  
• Compressor stations on gas transmission systems may not necessarily meter the fuel they draw from the pipeline. In these cases, the fuel consumption at the compressor stations either is estimated based on equipment duties or accounted as normal process shrinkage. Although not as common, similar situations can occur on oil transmission pipelines where product may sometimes be drawn from the pipeline to fuel the pumps. Theft, particularly from oil/natural gas systems, may be a significant unaccounted source of fuel use in some countries.

In theory, a thorough comparison of a Party’s Reference and Sectoral Approach calculations should identify most completeness issues. In practice, however, the energy statistics used for both approaches tend to come from the same government statistical agency, and therefore are likely to contain similar errors.