The parole, the oath of allegiance, and the amnesty oath were separate, unrelated issues. Each had different purposes, procedures and legal definition.

The parole was an agreement, normally written, signed and countersigned (occasionally verbal), between the two belligerents, that permitted a soldier who was captured or surrendered to be given his freedom, so long as he did not take up arms again until properly exchanged. This was the legal instrument of choice when large numbers of soldiers were involved -- such as the surrender of Vicksburg and Port Hudson, and the final surrender of the Confederate field armies. The verbage of the parole document was the result of a convention between the two armies.

The oath of allegiance was a Union document that permitted a prisoner of war, upon application made and approved, to be released from confinement after swearing an oath of allegiance to the United States, and permanently severing ties with the military forces of the Confederate States. This document was normally used in the Union military prison system. The applicant was interviewed and examined, and a recommendation made whether or not to approve his application. Not all applications were approved, and the decisions in those cases seem to be have been based on fairly subjective reasons.

The amnesty oath was a Union document used extensively toward the end, and after, the war. It was a modified Oath of Allegiance administered on an individual basis, and almost always approved. It was the legal basis for releasing Confederate prisoners at the end of the war, and after the war was used as an instrument to restore certain civil liberties.

All three documents are valuable research resources, because they usually, but not always, included a description of the individual soldier -- name, date and place of enlistment, age and nativity, physical description and place of residence.