Contract with variable quantity and fix price

depro

Hi Guys,

Our client has contracts with vendors for 1 year shipment of goods.
Contract Quantity is variable and do not depending on vendors.
Client doesnt know how many unit will be recive to warehouse during next year.
Let say in 2010 the quantity was 52, but in 2011 the quantity will be 49 units.
But the contract price is fixed.

This goods is being sold to customer based on the same contract type (fix price, variable quantity)
or customers buy goods per 1 item.

The problem is how to manage COGS during contract realisation becouse of:
1. invoice form Vendor is posted at the beginning of contract or during the recieve process (usually not after last recive)
2. invoice to Customer is created at the beginning of contract or during the shipment process (usually not after last shipment)

In other words we know how much we pay for 1 year contract and
how much we get from customer but we do not know how many items contract include.

Is there anybody with experience with similar case?
I would be appreciate for any ideas or suggestions.

regards,
Depro