The FIA International Court of Appeal has declared the double-decker diffuser designs used by Brawn GP, Toyota and Williams legal.
Following deliberation by the judges, the ICA has rejected the appeals lodged by Ferrari, Red Bull Racing and Renault, who claimed the design was against the regulations. BMW Sauber and McLaren had also entered the appeal as affected parties.
A statement issued by the FIA on Wednesday morning said: "Based on the arguments heard and evidence before it, the court has concluded that the stewards were correct to find that the cars in question comply with the applicable regulations."
The ICA's decision is a blow to those teams that did not pursue the design concept when they created their 2009 cars - as it is widely accepted that the double-decker diffusers have brought a performance advantage.