When two or more products are produced simultaneously by the same process up to a split-off point , they are called joint products.
For example, oil and natural gas are joint products.
When a company drills for oil, it gets natural gas as well.
The costs of exploration, acquisition of mineral right, and drilling are incurred to the initial split-off point
Such costs are necessary to bring crude oil and natural gas out of the ground, and they are common cost to both products.
Of course, some joint products may require processing beyond the split-off point.
For example, crude oil can be processed further into aviation fuel, gasoline, kerosene,naptha, and onther petrochemicals.
The key point is that the direct materials, direct labor,and overhead costs incurred up to initial split-off point are joint that can be allocated to the final product only in some arbitrary manner.