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.
But it appears the other Mercedes teams - the works outfit as well as Force India and Williams - are all using the currently-superior in-house fuel developed by Mercedes' title sponsor Petronas.
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.
In Barcelona, only Red Bull got the 12 horse power-better new Total fuel, with Renault customers Lotus, Toro Rosso and Caterham having to wait until this weekend in Monaco.
Reigning world champions Red Bull have reportedly calculated the advantage of the Barcelona fuel versus the previous spec at three tenths on the straight.
Indeed, while Mercedes' Nico Rosberg got his W05 up to 334.5kph on the straight, Daniel Ricciardo was not far behind, at 328.8.
Horner said: "If we can reduce our engine deficit by 50 per cent, we can beat Mercedes."