Related Rule
United States of America
Practice Relating to Rule 128. Release and Return of Persons Deprived of Their Liberty
Section C. Exchange of prisoners
The US Field Manual (1956) provides:
Exchange of prisoners of war, other than those whose repatriation is required by … [the 1949 Geneva Convention III], may be effected by agreement between the belligerents. No belligerent is obliged to exchange prisoners of war, except if a general cartel requiring such exchange has been concluded. The conditions for exchange are as prescribed by the parties thereto, and exchanges need not necessarily be on the basis of number for number or rank for rank. 
United States, Field Manual 27-10, The Law of Land Warfare, US Department of the Army, 18 July 1956, as modified by Change No. 1, 15 July 1976, § 197.
In 1994, during a debate in the UN Security Council on the situation in Tajikistan and along the Tajik-Afghan border, the United States encouraged the parties to resume discussions with the intention of participating in additional exchanges of prisoners. 
United States, Statement before the UN Security Council, UN Doc. S/PV.3482, 1 January 1994, p. 9.
In 1995, during a debate in the UN Security Council on the situation in Bosnia and Herzegovina, the United States stated that an exchange of prisoners between the Bosnian Serb side and the Bosnian Government gave reason for hope. 
United States, Statement before the UN Security Council, UN Doc. S/PV.3591, 9 November 1995, p. 12.