Table having outstanding order value

Dear Friends,

We have order relates billing (no deliveries). I am trying to develop an ABAP report which shows the open sales orders with outstanding sales values.

I am using the table VBAK for sales order data and VBUK to find out the open sales orders. However in case of partially billed sales orders I am not able to find the outstanding sales value.

For example: Sales Order No 120119923 has net value 1000 USD. Created a partial invoice against sales order No 120119923 for 300 USD. My resport should show below along with other regular fields:

Sales Order No     Due Net Value

120119923             700

I am not sure which table would have 700 as in above example.

Thanks & Regards,

Rajesh Singh