Sebastian Vettel is vowing not to give up on the 2009 Formula 1 World Championship title, despite racking up his fifth retirement in eleven races during the European Grand Prix at Valencia.

Although Jenson Button could only add two points to his advantage at the top of the drivers' table around the Spanish street circuit, Vettel's engine failure – his second of the weekend – has seem him slip 25 points adrift in the race for this year's title.

Retirements have become a regular feature of Red Bull Racing driver's 2009 F1 campaign, his failure to finish in Valencia signalling a fifth DNF in eleven races, the German signalling his frustration by claiming it was an engine blow for the 'umpteenth time' this year. By contrast, Button has scored in every race this season.

“The disappointment still lingers, that's for sure,” he told the official Formula 1 website.” When I recap the race I have to say that the start was quite good. Kimi Raikkonen got me but I was able to find my place in the field and by the end of my first stint I was able to regain ground on him and had a comfortable edge on Nico Rosberg.

“When I pitted to refuel there was no indication that something was going wrong, but when I left the pit I was surprised how well the tyres worked, and I found it a bit strange that the car was not laying lower. When I was braking I discovered perfect grip and the last thing that would have come to my mind was that I had effectively no fuel on board.

“After half a lap I was told about that fact and that I had to pit again to refuel. At that point that was the end of the race I had in mind. But then to discover some laps later that this was not the end of the story - my engine blew, for the umpteenth time this year.”

While Vettel stresses that he doesn't understand why he has been at the receiving end of such dismal reliability in 2009, the two-time race winner is retaining a positive frame of mind for the remainder of the season.

Indeed, with six races – and a total of 60 points – remaining, Vettel says he still 'believes' in his chances, starting with the next round at Spa-Francorchamps in Belgium.

“I still think that I am in the race for the title. And be sure, I will not give up fighting for it. True, it isn't ideal - not finishing five out of 11 races cannot be considered ideal - but I still believe in my chances.”