Sebastian Vettel prospered in Austin's clearer weather conditions to head the second practice session of the United States Grand Prix from teammate Mark Webber.
Ferrari driver Fernando Alonso had clocked the fastest time in first practice, when fog and technical problems with the medical helicopter disrupted proceedings.
The already-crowned world champion could only record the 18th fastest time in the morning, but was back on top in the afternoon after going round the Texas circuit in 1:37.305.
His Red Bull colleague Webber was his nearest rival, and they were followed on the timesheets by Mercedes pair Nico Rosberg and Lewis Hamilton, who finished third and fourth respectively.
Alonso could not match his performance from the first session, slipping down to 10th on the leaderboard, behind both Lotus Renault and Sauber drivers, as well as McLaren's Jenson Button, who came second to the Spaniard on the previous drive.
Second practice full standings:
1. Sebastian Vettel [Red Bull]
2. Mark Webber [Red Bull]
3. Nico Rosberg [Mercedes]
4. Lewis Hamilton [Mercedes]
5. Heikki Kovalainen [Lotus]
6. Esteban Gutierrez [Sauber]
7. Niko Hulkenberg [Sauber]
8. Romain Grosjean [Lotus]
9. Jenson Button [McLaren]
10. Fernando Alonso [Ferrari]
