The Green Gas Certification Scheme (GGCS) issues, transfers and retires Renewable Gas Guarantees of Origin (RGGOs) within our registry. RGGOs are issued to green gas producers for units of green gas injected into the gas grid, which displace units of fossil gas. They can then be transferred between a variety of counterparties before being retired and allocated to gas consumers. The GGCS ensures that only one RGGO is issued for each unit injected, that they are transferred securely, and only ever allocated to one consumer. By doing so we provide certainty that green gases are not double counted.