Okla. Admin. Code § 785:4-5-1
When deemed necessary and proper for the purposes of a hearing, pre-hearing discovery by an interested party may be allowed by the Hearing Examiner as provided under the APA and the rules in this Chapter. Depending upon the nature of the hearing, pre-hearing discovery may be requested at any time subsequent to the filing (and acceptance for filing) of an application or petition, or otherwise, at any time subsequent to the institution of proceedings on the application. The party requesting discovery shall submit a proposed schedule for discovery to be agreed upon and signed by the parties and for approval and signature by the Hearing Examiner. The joint schedule may include, but need not be limited to, requests for discovery, objections to discovery requests, responses to discovery requests to which there are no objections, exchange of exhibits to be introduced at the hearing, and a list of witnesses that may be called at the hearing. The parties may agree to close discovery in the proceedings under the joint schedule within a reasonable time before the date of the hearing, but not later than fifteen (15) days before the hearing. The Hearing Examiner must resolve disputes regarding discovery or disputes regarding compliance with the joint scheduling order as soon as possible so that the parties may continue to comply with the joint scheduling order. Requests for pre-hearing discovery must be timely made and the Hearing Examiner may impose reasonable and necessary limitations on the scope of discovery and the period of time within which discovery requests may be presented and entertained.
Okla. Admin. Code § 785:4-5-1