Giant oil spills making a sort of design (8)
I believe the answer is:
intaglio
'a sort of design' is the definition.
(type of engraved design)
'giant oil spills' is the wordplay.
'spills' is an anagram indicator.
'giant'+'oil'='giantoil'
'giantoil' anagrammed gives 'INTAGLIO'.
'making' acts as a link.
(Other definitions for intaglio that I've seen before include "Seal with a sunken design" , "Ligation (anag.)" , "Art of incised carving" , "favoured artist's technique" , "Carving in which design is sunken below surface" .)