By Lawrence Barretto - BBC Sport
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So that's just about it from me. Thanks very much for your company and contributions, as always, and I do hope to see you tomorrow for live text coverage of final practice and the all-important qualifying hour for the United States Grand Prix. Until then, have a great evening and I'll see you tomorrow at 1430 GMT. See ya.
Here's Andrew Benson's second practice report and do keep an eye on the website later this evening for a video highlights package of all the action. We'll also have plenty of analysis and reaction, too. There will be no Inside F1 this weekend, though, because of the time difference.
So it looks like Red Bull have the edge on pace - like they have done in the last five races - with Sebastian Vettel looking mighty despite his problems with the car in second practice. The McLarens looked strong on race pace, while championship contender Fernando Alonso was right in the mix.
And here's 13-24:
13) Grosjean 14) Perez 15) Ricciardo 16) Vergne 17) Hulkenberg 18) Di Resta 19) Kovalainen 20) Glock 21) Petrov 22) Pic 23) De la Rosa 24) Karthikeyan
Here's how they finished 1-12:
1) Vettel 2) Webber 3) Alonso 4) Hamilton 5) Button 6) Massa 7) Rosberg 8) Senna 9) Kobayashi 1) Schumacher 11) Raikkonen 12) Maldonado
*SEBASTIAN VETTEL FINISHES FASTEST IN SECOND PRACTICE FOR THE UNITED STATES GRAND PRIX*
Williams tell Pastor Maldonado to stop the car as he enters the pit lane. He does so, slotting it into neutral and rolling down towards his garage. Replays show that a flame burst out from the right hand side of the engine.
Sebastian Vettel is not invincible as the German locks his front left and runs wide, taking to the escape road at Turn 12. No real harm done, apart from his pride, and the championship leader continues on his way.
Long runs look to be the order of the day to end this session which means Sebastian Vettel looks set to do the double in Austin. Encouragingly for the race, Lewis Hamilton looks very quick on with a heavy car.
It's been a good performance from Bruno Senna who is currently eighth fastest in the Williams. He's 1.8 seconds off the pace, but 1.8 seconds faster than his team-mate Pastor Maldonado. That'll boost his confidence.
Every single car is out on track now as we enter the final 10 minutes of the session. Sebastian Vettel leads the way by seven tenths of a second from Mark Webber, Fernando Alonso, Lewis Hamilton and Jenson Button.
It looks like Mercedes have filled up Michael Schumacher's car with fuel to get some data on long runs as he's lapping around 10 seconds slower than he was earlier in the session.
Felipe Massa gets some advice from race engineer Rob Smedley about how to tackle Turn One. It seems he's braking later than his team-mate and turning which is something the Pirelli tyres don't like to do. Alonso keeps the tyres more straight he is told.
Clearly, there's no stopping Sebastian Vettel. The German spent much of this session sitting around while his team fixed a water leak. That would put many drivers on the back foot, especially when racing at a brand new track, but not Seb. Nope, he just flicks the visor down, gets into the zone and puts the hammer down. The German leads the field by seven tenths of a second. Yes, seven tenths of a second. Crikey.
So Mark Webber leads from Lewis Hamilton, Jenson Button, Sebastian Vettel, Felipe Massa, Fernando Alonso, Nico Rosberg, Bruno Senna, Michael Schumacher, Kimi Raikkonen and Romain Grosjean.
Ferrari on Twitter: (external) "It looks difficult to make the options work for Fernando."
Lewis Hamilton improves to the second fastest time, just under three tenths of a second off the pace. It's a decent first lap back on track from Sebastian Vettel, too, as the German clocks a 1:38.894 to go fourth quickest, four tenths off the pace.
It looks like Red Bull have fixed Sebastian Vettel's car as the reigning world champion is back out on track. The German has only completed five laps, while the majority of the rest of the field have completed 20 laps or more.
Jean-Eric Vergne has lost part of his front wing after Heikki Kovalainen cuts across him in the Caterham. The Frenchman waves his hand in frustration, but the Finn has troubles of his own. His left rear tyre has been punctured and and he's got to drive most of the lap with the rubber hanging off the rim if he is to return to the pits.
It's another improvement on his next lap for Webber as the Australian goes even faster, shaving another four tenths off his previous best to extend his lead to half a second. That's approximately three tenths slower than his Red Bull team-mate Sebastian Vettel managed this morning.
Mark Webber of Red Bull puts on a set of medium tyres and takes top spot away from Ferrari's Felipe Massa with a time of 1:38.958.
Kamui Kobayashi isn't having the best of times either. The Japanese driver has parked up his Sauber while the team fix a broken exhaust.
Peter Thomas on Twitter: (external) "I think this track is quickly going to be one of the classics - it's right up there with Spa & Suzuka. If only it had Spa weather..."
It's been a while since I've written this, but Felipe Massa has gone quickest in the Ferrari. The Brazilian goes two tenths quicker than Mark Webber's Red Bull, with his team-mate Fernando Alonso a couple of tenths further back in third.
Lewis Hamilton has a big snap of oversteer and spins the McLaren round. Lovely control, though, as he keeps the rear tyres lit up so he can keep the car rotating and pointing back in the right direction. That lap is obviously ruined, but no real damage done.
Red Bull confirm that Sebastian Vettel's car has suffered a water leak. The German is still out of the car while mechanics mop up the floor with paper towels.
Webber goes even quicker on his next lap, putting two tenths between him and Alonso after the Spaniard fails to improve despite setting the fastest middle sector of all.
Red Bull's Mark Webber is our new leader. The Australian clocks a 1:39.485 to head Ferrari's Fernando Alonso by just 0.005 seconds.
Lilli in Herts, via text: "I've fallen for CoTA quicker than a Red Bull in qualifying. SUCH a beautiful circuit!"
"Sebastian Vettel's Red Bull is up on its stands and the floor [of the car] is unceremoniously on the floor. They're working hard and fast to sort this problem with five or six mechanics underneath the car but I don't think he's getting out anytime soon."
Good picture from Williams on Twitter here which shows the huge turnout in Austin (external) - and this is only practice...
James on Twitter: (external) "I predict massive first corner crash! That first corner, skippy track, blind bend it's going to be wild."
The medium tyre - the softer of the two compounds available in Austin this weekend - have been bolted on to the Caterhams of Heikki Kovalainen and Vitaly Petrov. That'll be the first time we've seen that rubber this weekend.
Felipe Massa has hooked up a tidy lap to go second quickest, two tenths slower than Nico Rosberg in the Mercedes. Romain Grosjean has slotted into eighth in the Lotus, ahead of a strong showing from Toro Rosso's Daniel Ricciardo.
Hmmm, looks like the problem on Sebastian Vettel's Red Bull might take a while longer than the team first expected as the German has now climbed out of the car while the engineers continue to work on the car.
BBC Radio 5 live pit lane reporter Jennie Gow reports Sauber's Sergio Perez was given a reprimand for blocking Timo Glock in the Marussia during first practice.
Felipe Massa sets personal bests in all three sectors to go sixth quickest, nine tenths off the pace and around four tenths slower than Ferrari team-mate Fernando Alonso. Nico Rosberg retains the quickest time, ahead of Mark Webber and Alonso.
After Sebastian Vettel set his early quick lap, he headed straight back to the pits. It has since emerged that his Red Bull team were concerned about a problem with the car's water system. The mechanics are hard at work at the moment, while the championship leader can only sit in the cockpit and wait.
Fernando Alonso's Ferrari looks a bit of a handful, but the Spaniard still manages to get a lap time out of it as he goes quickest. Seconds later, Mark Webber and then Nico Rosberg knock the championship contender down a couple of pegs. Very competitive out there at the moment.
But Hamilton's next effort is good enough, just. It's 0.046 seconds quicker. His time at the top doesn't last long, though, as Mark Webber and then Jenson Button go quickest. Nice and close at the top at the moment, with just 0.06 seconds splitting the top three.
Lewis Hamilton's first effort is eighth tenths slower than Vettel's best which puts him second fastest overall, ahead of Sergio Perez, Daniel Ricciardo and Jenson Button.
Bang. Sebastian Vettel wastes no time in taking his place at the top of the timesheets in the Red Bull - but it's still some way of the pace he set in the first session.
"Everyone expects Red Bull to continue their recent dominant form this weekend but Mark Webber said it might not be as simple as that. All the recent races Red Bull have dominated have been held in hot conditions, but it's only about 19-20C in Austin this weekend, which may well have an impact on the way the tyres work. Webber said: '[Track] layout is not very important; temperatures are. If the black things on the corners are not working then [the car] is not going to work.'"
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