Only Kimi Raikkonen has shown consistency with a win and two second-place finishes, putting the Finn 10 points behind Vettel after four races. But no one else is close, which is a major contrast to last year's wide-open championship when four drivers were within 10 points of Vettel heading into Europe.
Vettel is still short of his 2011 form — when he had 93 points after winning three of the first four GPs — but he's notoriously hard to stop once he builds momentum.
"It's good to be back in Europe and in Spain in particular," Vettel said. "The whole Barcelona circuit is interesting as it includes all types of corners and offers a really good mix. But my favourite part is still the first sector because it has really quick corners."
Raikkonen, the 2007 F1 champion, needs a strong grid position — which has proved difficult so far — because overtaking is tricky on the Circuit de Catalunya, although the introduction of two DRS zones should help.
"I have won twice in Barcelona and I was on the podium there last year too, so I really look forward to going there again," Raikkonen said. "It's a circuit where you have to get everything exactly right to be at the top. All the teams have tested many times at this circuit, so to get an advantage there is not very easy. The setup is crucial as the track changes with the wind and temperature."
Two-time champion Fernando Alonso won in China and finished second in Australia but failed to finish in Malaysia and was a disappointing eighth in Bahrain, putting him already 30 points from Vettel in fourth place.
Lewis Hamilton's move to Mercedes is showing promising signs, yet he is 27 behind Vettel in third spot and Jenson Button is 10th for a struggling McLaren team. It, like the Red Bull, has been affected by tensions between teammates.
"It's been difficult for the team to make consistent progress," said Button, who was unhappy with Sergio Perez's aggressive driving when they were vying for points in Bahrain and recently had clear-the-air talks with the driver.
Vettel came out on top in his internal tussle with teammate Mark Webber, avoiding punishment despite ignoring team orders and overtaking the Australian to snatch victory in Malaysia. Having won that power struggle — Red Bull chose not to discipline their star, Vettel celebrated by winning in Bahrain to stretch his lead over Raikkonen.
Vettel, the youngest triple champion in F1 history, has 77 points so far. A far better start than last year, when he had 53 points in four races but still managed to beat Alonso for the title.
Alonso has six podiums at the Spanish GP but has not won it since 2006.
He needs to exert some pressure on Vettel, and is counting on some help from his home fans.
"The wins at Barcelona in 2006, Monza in 2010 and Valencia last year are unquestionably the races that have given me the best emotions of my career," said Alonso, who was second here last year. "From the first laps on the track on Friday and Saturday morning, you can immediately feel the passion of the fans in the grandstands and that sparks off extra motivation."
Mishaps have cost Ferrari points so far and chief designer Nikolas Tombazis hopes upgrades will improve reliability.
Lotus' upgrades will be a new front wing endplate, new aerodynamics around the rear drums, modifications to the diffuser and a different top rear wing, while Mercedes needs to add pace.
"A lot of effort is being put in to close that gap to the front-runners," Hamilton said.
Pirelli tires have been under the spotlight recently for wearing out too quickly, and teams will get an extra set of hard tires for practice sessions to ensure drivers run for longer, rather than conserving tires for the race.
Also, F1 officials will reportedly meet in Barcelona to discuss a potential new system that could lead to drivers facing race bans for repeat misbehaviour. The new system could replace grid penalties and fines that are currently levied against drivers for reckless driving.