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evaluation of results that are derived from stable compounds which are not affected by 
weathering processes. In addition, all measurements are subject to an analytical error. Thus, in 
order to be able to decide whether the data of two samples differ significantly or not, the 
analytical error of the individual measurement must be known. 
A When objective numbers, representing compound relations, are used for result 
verification in Oil Spill Identification, quality assurance plays the dominant role. 
The analytical error of each parameter must be determined statistically, and it 
must be ensured that the single measurements are randomly distributed about the mean. 
2 Methodology 
The method commonly used to identify oil types in Oil Spill Identification is GC screening. 
GC screening reveals the boiling range of oils, and oil types are - in a first approximation- 
characterized by their boiling ranges. However, additional GC/MS data are required in 
doubtful cases. GC/MS is used in any way when samples have to be compared in more detail. 
Oil types can be identified using the step-by-step method given below, i.e. by going through 
paragraphs 2.1 to 2.5, and in many cases a quick look at the screening results (GCs) should be 
sufficient to answer the question as to whether an unknown sample belongs to a specific type 
or not. 
Changes of spilled oil due to weathering have been particularly taken into account in this 
scheme, so that it should be possible to identify the type of an oil even in (highly) weathered 
samples. 
2.1 Light fuel oil (gas oil, diesel, fuel No 2) 
The vast majority of commonly used light fuel oils consist of “straight-run” gas oils or 
vacuum gas oils, i.e. products from atmospheric or vacuum crude oil distillation. Light fuel oil 
thus can be normally regarded as the mid-boiling cut of crude oil (“middle distillate”). 
Light fuel oil is ubiquitously used as bunker oil in ships of all sizes, from small pleasure craft 
to the biggest container ships or tankers. But the origin of light fuel oil may also be land based 
sources such as storage tanks or diesel engines. 
Therefore, the “identity” (or “match”) found between a spill sample and a comparison sample 
often is not very meaningful because there may be many possible sources of a light fuel oil 
spill. For example, a particular batch of light fuel oil from a bunker station supplies many