Despite Felipe Massa questioning Mercedes' engine equality, Pat Symonds is confident Williams are racing the same-spec as the Merc works team.
Following the Australian GP, in which he was beaten to the final podium position by Ferrari's Sebastian Vettel, Massa raised doubts about whether Williams were running the same engine specification as Lewis Hamilton and Nico Rosberg.
"If we don't have the same engine – which I cannot say 100 percent because it's very difficult to say – but if we don't have it then we want to have it because it's not nice that we don't have it," said the Brazilian.
However, Williams chief technical officer Symonds has rubbished that speculation, adamant the Grove team's cars are powered by the engines that are in the W06.
"We have no doubts over the parity of the engines from Mercedes during the Australian Grand Prix," he told Autosport.
"We have a great working relationship with all the team at Brixworth and know how hard they pushed things to the limit to bring the best performance to Australia.
"HPP are constantly checking the data and all the power units are exceptionally close in performance.
"Our aim now is to continue developing the car to ensure we can fight Ferrari."
Force India's deputy team boss Bob Fernley was also asked about engine parity and revealed it was part of his team's contract with Mercedes.
"Yes, and the contract states that," he told the publication. "All fairness to Mercedes, they have always been straight with us."