where joint supply exists the supply and demand for each product is linked to the others originating from the same source for example if demand increases for wool and sheep farmers therefore raise more animals for wool there will be a related increase in sheep meat production this increased production will lead to greater meat supply and potentially lower prices 
in some cases the proportions of the joint products are nearly fixed such as with cotton and cottonseed in such cases proportions cannot be varied in other cases the proportion can be variable for example through cross breeding it is possible to breed sheep either for wool or for meat so the quantity of one can be increased at the expense of the other to a degree analysts keep a close eye on products in joint supply because investments in one can be significantly impacted by what happens with the other another important issue with joint supply products is the allocation of expenses since both products are derived from the same source it is often difficult to figure out how to divide up expenses it is not usually feasible to simply split the expenses down the middle in the case of two products because one product usually sells at a premium to the other an equal split will artificially deflate or inflate profits on one product or the other likewise randomly allocating expenses will produce artificial results to handle this on the business side there are usually pricing matrices that work backwards from the end products to establish costing for reporting purposes joint supply vs joint demandjoint demand isn t necessarily related to joint supply rather joint demand happens when demand for two goods is interdependent for example printers need ink to function similarly ink cartridges are of no use without a printer another example could be razors and razor blades or gasoline and motor oil basically joint demand is when you need two goods because they work together to provide a benefit for the consumer if two goods are in joint demand they will have a high and negative cross elasticity of demand in other words a fall in the price of ink may prompt an increase in demand for printers 