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.

Econometric studies have recently shown an apparent contradictory evidence regarding substitution possibilities between energy (E) and capital (K). An analytical and empirical interpretation of E-K complementarity consistent with basic microeconomics and with the manufacturing process engineering evidence of E-K substitutability is presented. The notion of utilized capital is developed, and some of the seemingly disparate econometric findings are reconciled. The analysis emphasizes to the authors that care must be taken in interpreting and properly comparing alternative elasticity measures. 42 references. (MCW)