But in China, both Red Bulls were actually beaten by Fernando Alonso's resurgent Ferrari, following a disappointing opening three races for the Italian team.
Marko thinks Ferrari sped up thanks to a new blend of Shell fuel.
"We are also hoping to soon get a fuel that is more efficient," Marko said earlier this week, amid reports Red Bull's current Total fuel may be damaging the mandatory fuel flow sensors.
Marko has now told Germany's Bild newspaper: "Ferrari made a clear leap forwards in China. They have a new fuel. And we'll have some new fuel soon as well.
"Maybe we will have it at the next race in Spain," he revealed, amid engine supplier Renault's obvious horse power disadvantage early in 2014.
"The new petrol will bring us two, maybe even three tenths," added Marko. "So that we can have at least a chance of overtaking Ferrari.
"On Sunday (in China), our drivers could have done whatever they wanted, but they could not have passed Alonso," he said.