Open PO for cost center

Hii..

I have the flowing scenerao

my clint has 10 number of trucks as cost entre, all the expence for fuel, maintainance for truck is booked gainst cost centre.

Now i have an agreement with a vendor who has a gas filling station, the trucks goes to filling station and fills the gas, every time when required.

at the end of month for all the cost centre the toatal amount of fuel consume is sent to the client.

and he has to pay the vendor for total amount for fuel purchased and book the cost of fuel against each cost centre.

How do i map this scenerao..

Regards

sarfraz