A data processing system attributes energy consumption to individual program segments or threads includes a processor that executes a first thread during a first portion of a measurement interval and a second thread during a second portion of the interval. An energy monitor measures the total energy during the interval. Energy attribution code attributes a first amount of the total energy to the first thread and a second amount to the second thread based in part on the execution times of the threads. The code may define a range of possible energy values by determining maximum and minimum energy constraints for the threads. The invention may also be extended to a multiprocessor environment and to a simultaneous multithreading (SMT) processor. In addition, the process may be expanded to determine energy consumed by various peripheral units such as hard disk controllers and the like.