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2.5 Crude oil 
The pollutant must be crude oil if all other product types have been excluded by analysis. 
Crude oil spills may be caused by crude oil tankers or may originate directly from crude oil 
production, where feasible. 
For example, the finding that crude oil is involved in an oil spill in the congested shipping 
area of the German Bight means that all ships except tankers can be excluded as possible 
sources. Crude oil from tank washings of tankers often can be identified by the presence of 
additional higher-boiling n-alkanes (wax): these compounds adhere to the tank walls after 
unloading. They are washed out by means of, or together with, residues from the original 
cargo (“crude oil washing”). But direct input from oil production can be definitely excluded if 
a non-North Sea crude oil is found. Moreover, experience has shown that even rough further 
classification by crude oil types may narrow down considerably the number of possible 
sources, even to a single ship. The classification of crude oils by their main production areas 
by means of a database of crude oils thus is the first step toward identifying the source of an 
unknown crude oil pollution. Crude oils are transported mainly in the form of mixed oils or 
blends (Brent mix, Flotta mix) in which the geochemical differences characterizing single 
platforms are levelled out. Nigerian light, Russian export blend, Arabian or Iranian light or 
heavy, are each produced from numerous single wells. Their broader characteristics reflect 
their general production area. 
On the other hand, environmental controlling or monitoring of platforms is an entirely 
different task. Of course, broader characteristics are only of very rare value when an oil spill 
in a distinct production area is suspected to have emanated from one of the surrounding 
platforms. Oil spills from oil production primarily emanate from offshore tanker loading 
(where the oil is not carried ashore by pipeline), pipeline leaks or wellhead leaks. Pipelines 
may carry crude from a single or multiple oil fields (blends). 
2.5.1 Analysis 
Crude oils contain characteristic compounds or compound relations which are typical of their 
origin in the world's main production areas, such as the Middle East or North Sea, in a 
particular oil field or even a single platform. 
A The following findings are based on a collection of 260 samples from crude oils 
transported or produced in Europe. This collection allows some general 
conclusions regarding the different crude oil types, although exceptions are, of 
course, possible.