Invoice Price Variance Issue

Hi Experts,

                   I have a Issue where the there is a Price Variance of Invoice with Price of PO. with which am unable to validate the Invoice. Please provide all the possible solutions for this recurring Issue.

Scenario:-

I have PO for Fuel Consumption, Once I receive a Fuel, we start consuming all the Fuel immediately, later when we receive the Invoice, there is  a price variance of Invoice with PO, now I cannot return the PO as the Fuel has got consumed, Please advise in this regard.