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Annex 4 231
IEA sources of uncertainties that can be quantified for this work
As mentioned in Section 1.5.1 of the main report, IEA energy balance statistics represent the best available
top-down numbers that include marine bunker fuels estimates on a global basis. We assess the quality of IEA
by looking at possible sources of uncertainties, and by estimating the potential correction when it is feasible.
We identify four important sources of top-down marine fuel uncertainties:
1 Maritime sector reporting: fuel sales distinguish between international and domestic navigation
categories with uncertainty. Errors can be made when fuels reported under different categories are
combined. This type of error can be spilt in two cases:
a
b
Misallocations: Fuels that should be attributed to national navigation are allocated in international
navigation or vice versa. In this case, only the total (sum) of sales per type of fuel is correct, while
the allocation is uncertain.
Duplications: Fuel sales could be allocated in both categories, double-counting the amount of
fuel sold. In this case, the allocation and fuel totals can contain errors contributing to uncertainty.
2 Other sector misallocation: marine fuels might be allocated to other non-shipping categories, e.g.
export, agriculture, etc. In this case, marine fuels would be under-reported and other sectors may
have their fuels over-reported.
3 Transfers category reporting: in accordance with IEA, this category comprises inter-product transfers,
which result from reclassification of products either because their specification has changed or
because they are blended into another product. The net balance of inter-product transfers should be
zero; however, “National stocks” can be used in blending residual bunkers to specification. This could
increase the volume of fuel delivered to ships sometimes without statistical documentation (IEA,
2013), resulting in under-reporting.
4 Data accuracy: IEA data may suffer a lack of intrinsic accuracy because of the ways in which the data
are collected.
These sources of discrepancy are not mutually exclusive, and not all of them can be identified and quantified
given available data at the national levels.
Estimates of potential adjustment to top-down statistics
Potential adjustments are evaluated by considering world energy statistical balances, and quantifying
discrepancies in quantities most related to known top-down uncertainty. We quantify sector misallocation
specifically for cumulative volumes that could be misallocated marine bunkers, in whole or in part.
Export-import misallocation
Some of energy allocation discrepancies can be identified through analysing IEA data in world balance format.
We use these discrepancies to estimate potential corrections due to uncertainties that are under the category
“other sector misallocation”.
As acknowledged by IEA, the difference between total exports and imports (net difference at world scale)
indicates a possible misallocation of bunkers into exports for some countries. By collecting IEA data in
world balance format, this net difference at world scale can be used to identify an upper bound of potential
correction. Given evidence that at least part of this discrepancy could be from a misallocation of marine fuels,
we expect that the best estimation of this uncertainty would adjust the fuel sale data. In other words, if excess
exports are not recorded as imports, then excess fuel deducted as exports could be sold as marine bunkers
without record.
The net discrepancies reported by IEA as “Statistical differences” are calculated as total consumption minus
total supply. Figure 20, Figure 21 and Figure 22 show the marine fuel sales data and both discrepancies over the
period 1971–2011. The net statistical difference should be expected to be smaller than any single contributor
to the net differences. This is because net statistic difference includes the export-import discrepancy, and all
other discrepancies that may be additive or offsetting, including unquantified discrepancies (uncertainties) in
marine bunker statistics.