A joint product is any product that comes out of a manufacturing process alongside other products, where all of them have significant market value and none can be produced without the others. When a petroleum refinery processes crude oil, it inevitably produces gasoline, diesel fuel, jet fuel, and several other products simultaneously. No refiner can choose to make only gasoline. These products are joint products because they share a single production process, use the same raw materials, and each carries real economic value.
How Joint Products Work
Joint products start as the same input material and remain inseparable through the early stages of production. At some point in the process, individual products become distinguishable from one another. That moment is called the split-off point, and it’s the most important concept in joint product accounting.
Before the split-off point, all production costs are pooled together as “joint costs” because there’s no meaningful way to assign them to any single product. After the split-off point, each product takes on its own identity and may undergo additional processing, packaging, or refinement with costs that belong clearly to it. The split-off point determines how shared costs get divided among the products and influences whether a company should sell a product immediately or invest in further processing.
Real-World Examples Across Industries
Petroleum refining is the classic example. According to U.S. Energy Information Administration data from 2023, a single 42-gallon barrel of crude oil yields about 19.6 gallons of finished motor gasoline, 12.5 gallons of diesel fuel, 4.4 gallons of jet fuel, and smaller quantities of petroleum coke, hydrocarbon gas liquids, asphalt, lubricants, waxes, and more. All of these come from the same barrel through the same distillation process. A refinery cannot produce jet fuel without also producing gasoline and diesel.
Dairy processing follows the same pattern. Raw milk is separated into cream and skim milk, which then become butter, cheese, whole milk powder, nonfat dry milk, and other products. The raw milk is the shared input, and the separation process creates multiple valuable outputs.
Meatpacking is another straightforward case. A single pork carcass is broken down into primal cuts: the loin, ham, belly, Boston butt, and picnic shoulder. From those come retail products like spareribs, back ribs, sirloin, and ground pork from the trim. A processor buying the whole animal produces all of these cuts together. There is no way to raise a pig that yields only bacon.
Joint Products vs. By-Products
The distinction comes down to economic value. Joint products all have significant sales value relative to the total output. By-products are secondary outputs that are salable but have only minor value compared to the main products. A by-product is produced incidentally, without being the reason the process exists.
Consider sawdust at a lumber mill. The mill exists to produce boards and beams. Sawdust is an unavoidable output with some market value (it can be sold for animal bedding or pressed into particle board), but it’s not why anyone runs the mill. That makes it a by-product. If the sawdust somehow became extremely valuable, approaching the value of the lumber itself, it would be reclassified as a joint product. The line between the two categories isn’t fixed. It shifts with market conditions.
How Companies Divide Shared Costs
The trickiest part of joint product accounting is figuring out how much of the shared production cost belongs to each product. If a refinery spends $5 million processing crude oil before the split-off point, how much of that cost belongs to the gasoline versus the diesel versus the jet fuel? There’s no objectively correct answer, which is why several allocation methods exist.
The most widely preferred approach is the sales value method, which assigns costs in proportion to each product’s market value. If gasoline represents 60% of the total sales value at the split-off point, it absorbs 60% of the joint costs. The reasoning is intuitive: a product’s market price is the most reliable indicator of its economic value, so it should bear a proportional share of the costs that created it.
Sometimes a product can’t be sold at the split-off point because it needs further processing first. In that case, companies calculate a hypothetical market value by taking the product’s final selling price and subtracting the cost of any processing done after the split-off point. This gives an estimate of what the product would have been worth at the moment it became identifiable.
A simpler alternative is the physical measure method, which divides costs based on quantity, such as gallons, pounds, or units. If a process yields 1,000 gallons of Product A and 500 gallons of Product B, Product A gets two-thirds of the joint cost. This method is easier to calculate but ignores the fact that a gallon of jet fuel and a gallon of asphalt are worth very different amounts.
The Sell or Process Further Decision
One of the most practical decisions involving joint products is whether to sell a product at the split-off point or invest in additional processing to increase its value. The key principle here is that joint costs are irrelevant to this decision. Those costs are already spent by the time the split-off point arrives, regardless of what happens next. They’re sunk costs.
The only numbers that matter are the additional revenue from further processing versus the additional cost of that processing. If turning raw cream into butter adds $2,000 in revenue but costs $1,500 in extra processing, the $500 difference makes further processing worthwhile. If the extra revenue is less than the extra cost, the product should be sold as-is at the split-off point.
This analysis applies to each joint product independently. A company might find it profitable to further process one joint product while selling another immediately. The decision is always based on incremental costs and incremental revenue, never on how the original joint costs were allocated.
Why the Concept Matters
Joint products create real challenges for pricing, profitability analysis, and inventory valuation. Because the cost allocation is inherently somewhat arbitrary, the reported profit margin on any single joint product can be misleading. A change in allocation method can make gasoline look more profitable and diesel less profitable, or vice versa, without anything changing in the actual operation.
This is why managers who work with joint products focus heavily on the profitability of the overall process rather than obsessing over margins on individual products. The relevant question isn’t whether diesel is profitable on its own, but whether the entire refining operation generates enough total value to justify its costs. Individual product margins are useful for pricing guidance and financial reporting, but they reflect accounting choices as much as economic reality.