Several Eastern Mediterranean countries have formally established an intergovernmental organization to cooperate in developing the massive offshore natural gas fields in the region, conspicuously leaving out Turkey as a member state.

The East Mediterranean Gas Forum (EMGF) is to be based in Cairo and any East Mediterranean country can apply for membership, the Egyptian Ministry of Petroleum and Mineral Resources said Wednesday. Any other country, as well as any regional or international organization, can apply to join as an observer “provided that they share the same values and objectives of the EMGF,” the ministry said.

The ministry did not identify the countries that signed the agreement to formally charter the EMGF. Bloomberg reported the current member countries are...