Processed crude oil becomes more murky (8)
I believe the answer is:
cloudier
'more murky' is the definition.
('cloudy' can be a synonym of 'murky')
'processed crude oil' is the wordplay.
'processed' indicates an anagram.
'crude'+'oil'='crudeoil'
'crudeoil' is an anagram of 'CLOUDIER'.
'becomes' acts as a link.
(Other definitions for cloudier that I've seen before include "more dull" , "Less transparent or clear, liquid say" .)