This report responds to a recommendation from the Department of Energy's (DOE) Advisory Committee on Appliance Energy Efficiency Standards. It presents the derivation of estimated consumer marginal energy prices for the commercial and residential sectors for use in the life-cycle cost (LCC) analyses for four of the high priority appliances' energy efficiency standards rule makings --clothes washers, water heaters,fluorescent lamp ballasts, and central airconditioners/heat pumps. Marginal prices as discussed here are those prices consumers pay (or save) for their last units of energy used (or saved). Marginal prices reflect a change in a consumer's bill (that might be associated with new energy efficiency standards) divided by the corresponding change in the amount of energy the consumer used.