The letter addresses the need for allocating real power losses originated from multiple flow contributors who use the same transmission line. It is shown that the total losses can be classified as own-losses and cross-losses. It is the cross-losses that are difficult to allocate. The Occam's razor principle is used for allocating the cross-losses, resulting in the cross-losses proportioning (CLP) method. Mathematical proof is provided to validate the usefulness of the CLP method. The allocation of losses of this nature also has a long history in other economical and engineering problems, such as the allocation of natural gas losses in pipelines. Hence, the problem is a general one to be explored.