Fuel has emerged with a big role to play in F1's new V6-powered era.
Germany's Auto Motor und Sport said struggling Renault took a 12 horse power step forward last time out in Barcelona, thanks entirely to a new blend of fuel supplied by French partner Total.
And Red Bull team boss Christian Horner sees more gains to come.
According to correspondent Schmidt, it was at Red Bull's considerable expense that the new Total fuel was brought in line with homologation so that it could debut in Spain.
"We're talking about 20 horse power," he said. "Mercedes has the advantage -- you can see it in comparison to their customer teams."
According to correspondent Michael Schmidt, Horner may be referring to McLaren, who power their Mercedes V6 with fuel supplied by team sponsor Mobil.
Renault engine boss Rob White said: "With the turbo engines, the fuel suppliers started at zero, which is why we see these big leaps in performance at the beginning."
According to Italian reports, Ferrari president Luca di Montezemolo has also recognised the importance of fuel in 2014, urging the Maranello team to move closer to its works supplier, Shell.
Reigning world champions Red Bull have reportedly calculated the advantage of the Barcelona fuel versus the previous spec at three tenths on the straight.
Horner said: "If we can reduce our engine deficit by 50 per cent, we can beat Mercedes."