Industrial demand for energy is essentially a derived demand: the firm's demand for energy is an input is derived from demand for the firm's output. Inputs other than energy typically also enter the firm's production process. Since firms tend to choose that bundle of inputs which minimized the total cost of producing a giving level of output, the derived demand for inputs, including energy, depends on the level of output, the submitions possibilies among inputs allow by production technology, and the relative prices of all inputs.