Petrol suppliers in the US? (6)

I believe the answer is:

gasmen

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'the us?' is the definition.
Although both the answer and definition are plural nouns, I cannot understand how one could define the other.

'petrol suppliers' is the wordplay.
'petrol' becomes 'gas' (synonyms).
'suppliers' becomes 'men' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'gas'+'men'='GASMEN'

'in' is the link.

Can you help me to learn more?

I've seen this clue in The Irish Independent.

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