Page type: primary-anchored (mirrors RIIO-GT3 Final Determinations)

Last updated: 2026-04-05

RIIO-GT3: Gas Transmission Price Control 2026-2031

RIIO-GT3 is Ofgem's price control for National Gas Transmission, the sole owner and operator of the National Transmission System (NTS) in Great Britain. The NTS is over 7,600 km of high-pressure pipeline transporting gas from entry terminals to distribution networks, power stations, and large industrial users. The control runs from 1 April 2026 to 31 March 2031.

Key parameters

What National Gas must deliver

Asset health and resilience. GBP 930m funds replacement or refurbishment of ageing NTS assets, with evaluative PCDs introduced for compressor acoustic buildings, easement reinstatement, valve/pipe stabbings removal, and actuator replacement. National Gas must report quarterly on asset health progress. If work is not delivered, costs are returned to consumers (GT Annex 2.1, 5.22).

Network capability. The West Import Resilience Project (WIRP) PCD provides GBP 83.3m for an 11km pipeline in South Wales, expanding NTS capability for growing west-to-east LNG flows (GT Annex 5.11-5.12). A Network Capability Re-opener is available for further compressor performance upgrades and site reconfigurations.

Emission reductions. Approximately GBP 0.6bn is directed at reducing methane emissions from compressors and pipelines. New financial incentives (Greenhouse Gas Emissions ODI-Fs for compressors and pipelines) drive adoption of cleaner technologies. A Compressor Emissions PCD and Network Decarbonisation and Emissions Compliance Re-opener fund the transition (GT Annex 2.5, 3).

Strategic planning cooperation. A new licence obligation requires National Gas to cooperate with NESO and proactively share information for long-term gas system planning. This formalises NESO's increasing role in NTS resilience and strategic planning, including the Gas Network Capability Needs Report and Gas Options Advice that feed into the Centralised Strategic Network Plan (GT Annex 3; Overview 2.17-2.18).

System operation. GSO incentives drive performance on entry/exit constraint management, demand forecasting, residual balancing, maintenance, and customer satisfaction -- all with financial ODI-Fs (GT Annex 3).

How uncertainty is managed

RIIO-GT3 includes substantial uncertainty mechanisms reflecting both gas future uncertainty and the complexity of NTS investment:

• Asset Health Re-opener: three windows (Apr 2027, 2028, 2030) for emerging asset health needs including AC accelerated corrosion, new valve/site programmes
• Gas Strategic Planning Re-opener: for NESO/government-driven investments (Authority and licensee triggered)
• Network Capability Re-opener: compressor performance, site reconfiguration (Apr 2028, 2029)
• Network Decarbonisation and Emissions Compliance Re-opener: environmental and emissions investments
• WIRP Re-opener: for further phases of West Import Resilience
• Bacton Enhanced Filtration Re-opener: additional filtration for international flows
• Office/NCC/ECR Relocation Re-opener: critical infrastructure relocation (Apr 2026, 2028)
• Funded Incremental Obligated Capacity (FIOC): for capacity investment

Approximately GBP 1.5bn of additional requests expected through these mechanisms, excluding government/NESO-driven investment where need is still uncertain.

Gas future and depreciation

Unlike GD, GT depreciation is NOT accelerated. The existing 45-year sum-of-digits profile is retained for RIIO-GT3 (Overview 7.9). Three stakeholders supported this, including National Gas. The rationale: the NTS may have a long-term role in hydrogen or CO2 transport, and government decisions on gas future have not yet been made.

Ofgem will review GT depreciation when setting RIIO-4, informed by the government's future of gas programme. The government's upcoming call for evidence on network cost recovery will consider options beyond accelerated depreciation.

Cost assessment

As a single-licensee sector, GT cannot use comparative benchmarking. Ofgem relies on bottom-up engineering review of 31 EJPs. At Final Determinations, 7 were fully justified and 24 approved with adjustments (up from 6 and 22 at DD). Unit costs are set at the minimum of median historical cost plus 10% or the mean historical cost. Risk and contingency is capped at 10% of project cost, with no separate contractor risk premium (GT Annex 5.23-5.37).

The 39% TIM sharing factor (lower than GD's 50%) reflects greater cost uncertainty in a single-company sector with more bespoke, complex investments.

LNG and changing flow patterns

A structural shift in GB gas supply is driving investment. As domestic North Sea production declines, LNG imports are growing, creating west-to-east flow patterns on the NTS. The WIRP pipeline in South Wales and Network Capability Re-opener address this, ensuring the NTS can accommodate alternating flow patterns driven by LNG dependence (GT Annex 1.4, 2.2).

Defined terms

See the full defined terms register in the source file.

Cross-references

• Gas Act 1986 -- legal basis for Gas Transporter licences
• National Gas Transmission Licence -- being modified for RIIO-GT3
• Uniform Network Code (UNC) -- gas transportation arrangements
• NESO Gas Network Capability Needs Report and Gas Options Advice
• RIIO-3 Finance Annex -- cost of capital, debt, depreciation
• RIIO-3 SSMD GT Annex (July 2024) -- methodology framework
• Government Midstream Gas System Update (June 2025)
• RIIO-GD3 -- companion gas distribution price control (same RIIO-3 package)

Character positions

No character positions ingested yet for this instrument.