SECTION 5. DEFENSE OF THE TITLE
(a) Each WBO World Champion except in the Heavyweight Division shall defend his title at intervals not greater than nine (9) months counting from the date of the acquisition thereof or from the last compulsory defense, as the case may be, in a twelve (12) round fight, against the Mandatory Challenger, as determined by the Championship Committee according to these Regulations, unless an exception is made pursuant to these Regulations. For reasons unique to the Heavyweight Division, the WBO World Champion in the Heavyweight Division shall defend his title at intervals not greater than twelve (12) months counting from the date of the acquisition thereof or from the last compulsory defense as the case may be in a twelve (12) round fight, against the Mandatory Challenger, as determined by the Championship Committee according to these Regulations, unless an exception is made pursuant to these Regulations.
(b) In the interim period, the World Champion may defend the title against any contender classified within the fifteen (15) best by the World Boxing Organization, always with the approval of the World Championships Committee.
(c) The WBO World Championship Committee may, in its discretion, vacate a Champion’s title (including the Heavyweight Division) regardless of cause or fault if the Champion fails to defend his title within a nine (9) month period. This decision will be final unless appealed to the Complaint and Grievance Committee within ten (10) days of Notification to the Champion as provided for in these Rules. A Champion so stripped of his Title shall be classified using the WBO rating criteria, and he shall be classified in his division or in such other weight division as the Classifications Committee for good cause determines, provided that he has complied with the WBO and ABC rating criteria.
(d) No WBO Champion may hold titles in more than one Weight Division. If a WBO Champion wins a WBO Championship in a higher or lower division, the WBO Champion shall have Ten (10) Days to determine which Weight Division the WBO Champion will retain. The other Weight Division will be declared vacant.
(e) In any circumstance in which a Mandatory Defense does not occur within the designated time period, the World Championship Committee may order an Interim Championship between contenders determined by the World Championship Committee.
Regulations - WBO