Mercedes boss Toto Wolff feels Red Bull are losing out on performance because of their choice of fuel suppliers.
Red Bull are fuelled by ExxonMobil, but their engine supplier Renault use BP/Castrol.
And Wolff thinks their financially-driven decision is costing them valuable time on the track.
“ExxonMobil is capable of making a state of the art fuel, or BP/Castrol, or any of the top players,” Wolff said to Motorsport.com.
“The strategic mistake is to opt for the commercial deal rather than making sure you are on the same specification of fuel and oil as the works team.
“Our teams have always used Petronas, apart from McLaren. It was never a question, because strategically you need to make sure that you are on the same performance levels, and therefore have the same fluids, as the works team.
“We’re all using the same fuels, because we’re calibrating our engines on one spec of fuel. If you have a different spec of fuel, you need a completely different engine calibration.
“You’re running different calibrations on track, which doesn’t give you any learning. You’re making your life complicated if you’re having different specs. It’s a philosophy.”