Full-scale military exercises, or even smaller-scale ones, are not always feasible or even desirable. Availability of resources, including money, is a significant factor—it costs a lot to release troops and materiel from any standing commitments, to transport them to a suitable location, and then to cover additional expenses such as petroleum, oil and lubricants (POL) usage, equipment maintenance, supplies and consumables replenishment and other items. In addition, certain warfare models do not lend themselves to verification using this realistic method. It might, for example, prove counter-productive to accurately test an attrition scenario by killing one's own troops.