Temperature lowered initially in USA oil centre (5)
I believe the answer is:
tulsa
'oil centre' is the definition.
(I've seen this before)
'temperature lowered initially in usa' is the wordplay.
'temperature' becomes 't' (abbreviation).
'initially' says to take the initial letters.
'in' indicates putting letters inside.
The first letter of 'lowered' is 'l'.
'l' put inside 'usa' is 'ulsa'.
't'+'ulsa'='TULSA'
(Other definitions for tulsa that I've seen before include "Oklahoma city featured in a 1960s pop song" , "City in Oklahoma featured in a 60s song" , "OK city" , "US city" , "Where in the States" .)