43 CFR §3137.80

1. (a)Participating areas are those committed tracts or portions of those committed tracts within the unit area that are proven to be productive by a well meeting the productivity criteria specified in the unit agreement.
2. (b)You must include a description of the anticipated participating area(s) size in the unit agreement for planning purposes to aid in the mitigation of reasonably foreseeable and significantly adverse effects on NPR-A surface resources. The unit agreement must define the proposed participating areas. Your proposed participating area may be limited to separate producible intervals or areas.
3. (c)At the time you meet the productivity criteria discussed in § 3137.82 of this subpart, you must delineate those participating areas.