The prime assets of an oil and gas company are its reserves and resources; they are the most important information about a company, and are the basis on which capital is raised to carry out its activities. A reporting issuer is a company that sells securities on the open market, but not necessarily on an exchange. Cana- than National Instrument 51-101 (NI 51-101) governs the dis- closure that is required of a reporting issuer. It has been in force since September 2003 and mandates the disclosure of Proved and. Probable reserves and allows the disclosure of other categories of resources by reporting issuers. This paper provides a background to the securities regulation and regulatory reporting regime of NI 51-101, including recent amendments. It is not a substitute for the expert advice that should be sought by anyone attempting to fulfill securities regulatory requirements. Some trends and issues on oil and gas reserves and resource estimation and disclosure in Canada and the international arena are also discussed.