A person participates in a declared wholesale gas market in a registrable capacity if the person is—
(a) a service provider for the declared transmission system or for a declared distribution system; or
(b) a producer or blend processing service provider who injects covered gas into a declared transmission system or a declared distribution system; or
(c) a storage provider whose storage facility is connected to the declared transmission system or a declared distribution system; or
(d) a person who buys or sells covered gas in the declared wholesale gas market; or
(e) a person classified by the Rules as a participant in the declared wholesale gas market.