Break even, essentially, storing oil at complex (7)
I believe the answer is:
violate
'break' is the definition.
(I know that break can be written as violate)
'even essentially storing oil at complex' is the wordplay.
'essentially' means to look at the middle letters.
'storing' means one lot of letters goes inside another.
'complex' indicates anagramming the letters.
The middle of 'even' is 've'.
'oil'+'at'='oilat'
'oilat' anagrammed gives 'iolat'.
've' going around 'iolat' is 'VIOLATE'.
(Other definitions for violate that I've seen before include "Infringe; defile" , "Transgress" , "Rudely disturb" , "Desecrate, despoil" , "Profane" .)