What is the "Buyer On-sale Volume"?

"Buyer On-sale Volume" is a phrase that has been using in the LNG contracts.Somtimes buyers are not end users themselves and they sale to other smaller customers.In this case they need to get a seller's consent for selling the purchased cargo to smaller buyers upon the agreed contract.Such volume called as a "Buyer On-sale Volume".This means that seller give a flexibility to buyer for divert the total or some part of purchased cargo.This flexibility is much restricted.In the other word the seller give a such advantage to buyer just in the very small market that it does not threat his benefit.