Does Oil refineries use process costing?

Yes. depending on the type of crude that is processed actual output of the different type of product yield in % weght is determined through a material balance or bass balance process.

The total cost is then apportioned by the weight of each product yield. The weight is then converted to volume which is used in dividing the apportioned cost to arrive at the unit cost of each type of prouct yield from the refining process.