No further engine upgrade opportunities have been granted to Formula 1's power unit manufacturers following the third and final review period of the 2026 season, the FIA has confirmed.

Along with its all-new power units for the 2026 season, F1 introduced Additional Development and Upgrade Opportunities (ADUO) as a mechanism to allow less performant engines to be improved.

The sport's governing body announced on Tuesday that the gaps to the strongest performing engine had "evolved" over the period from round 12 in Hungary to round 18 in the United States, but not to a degree that would result in additional upgrades.

The first review period, which covered the first five races of the season, saw Red Bull adjudged to have the best performing engine, with Mercedes' 2-4 per cent deficit meaning they were granted one upgrade for the 2026 season and another for 2027.

The other three manufacturers - Ferrari, Audi and Honda - were found to be more than four per cent down on performance and were therefore granted two upgrade opportunities for this season and two more for next year.

As was the case this time around, the results from the second period did not lead to any additional homologations being granted.

An FIA statement said: "The FIA can confirm that the results of the third ADUO analysis period of 2026 (Races 12 to 18) have been communicated to all Power Unit manufacturers.

"For the third period, the relative performance gaps to the leading ICE evolved, but these changes did not result in any additional homologations being granted to the Power Unit Manufacturers.

"Due to the confidential nature of this information, no further details on Power Unit performance index measurements will be communicated."

The rankings after period one resulted in confusion because Mercedes had at that point won the first five races of the season, and were seen by most in the paddock to have the best overall power-unit performance.

ADUO measurements are specifically taken from the performance of the Internal Combustion Engine (ICE), which is only one element of the power unit.

The Mercedes works team completed a title double on Sunday in Brazil as the Silver Arrows closed out the Constructors' Championship a week after Kimi Antonelli had sealed the drivers' title.

It can be deduced from the FIA statement that Red Bull have not fallen two per cent behind any other team and that Mercedes have not fallen beyond four per cent behind the leading engine.

It is also theoretically possible that Mercedes, Ferrari, Audi and Honda could have reduced their deficits to Red Bull or even moved up to two per cent ahead of the Milton Keynes outfit.

However, that seems highly unlikely in the case of Mercedes because they have not used their 2026 upgrade opportunity yet, and for the other manufacturers because of their continued inferior performance on track.

Mercedes also supply engines to McLaren, Williams and Alpine. Ferrari have Haas and Cadillac as customers, while Red Bull supply junior squad Racing Bulls. Audi are only producing engines for their own team, while Honda exclusively supply Aston Martin.

FIA director of single seater Nikolas Tombazis said: "The FIA has undertaken extensive analysis as part of the review of ADUO this year. Based on the quality of the data and the robustness of the assessment process, we are confident in our findings and the conclusions reached.

"The first year of implementation has also reinforced our belief that the ADUO concept is the right one for Formula 1. However, it is important that the system continues to evolve to ensure it remains efficient, relevant and fit for purpose.

"To that end, we have been working closely with the Power Unit Manufacturers and teams to explore refinements to the methodology that will support the continued effectiveness of ADUO in future seasons."