The IPCC Good Practice Guidance provides some information on the likely causes and expected magnitude of uncertainties in a Party’s emission estimates from fuel combustion. You should remember, though, that an individual Party’s uncertainties can differ dramatically from the default values provided by the IPCC and that uncertainty values can be based on subjective judgments.

• Estimates based upon direct measurements from large point sources are expected to have an uncertainty of roughly +/-3 percent.
  
• Overall random errors in energy statistics (i.e., activity data) for Parties with rigorous data collection systems are expected to be 2 to 3 percent.
• Overall uncertainty, including systematic biases, in activity data for stationary combustion is expected to be on the order of 5 to 10 percent, although it can be significantly higher.

Table 2.6. Level of Uncertainty Associated with Stationary Combustion Activity Data