The 1991 United States Grand Prix (formally the XXVIII Iceberg United States Grand Prix) was a Formula One motor race held on March 10, 1991 in Phoenix, Arizona. It was the first race of the 1991 Formula One World Championship. The 81-lap race was won from pole position by Ayrton Senna, driving a McLaren-Honda, with Alain Prost second in a Ferrari and Nelson Piquet third in a Benetton-Ford.
The race marked the respective debuts of future double World Champion Mika Häkkinen and the Jordan team. It was also the first F1 World Championship race in which ten points were awarded for a win rather than nine, as part of a revised scoring system introduced for 1991. However, it was also to be the last United States Grand Prix until 2000, due to poor attendances.
In the two previous years, the championship had been decided when Senna and Prost tangled at Suzuka. In 1989, their collision as team-mates secured Prost's third World Championship; in 1990, with Prost driving for Ferrari and still in title contention, it handed Senna his second crown. Controversy regarding the nature of the 1990 incident had created great anticipation for the rematch.
Qualifying
Pre-qualifying report
Several teams were required to participate in the Friday morning pre-qualifying sessions during 1991, in order to reduce the field to thirty cars for the main qualifying sessions on Friday afternoon and Saturday. At the midway point of the season, the pre-qualifying group was to be reassessed, with the more successful teams (over a twelve-month period consisting of the second half of 1990 and the first half of 1991) being allowed to avoid pre-qualifying thereafter, and less successful teams being required to pre-qualify from mid-season onwards.
Eight cars were to take part in pre-qualifying sessions during the first half of the 1991 season, after 1990 ended with no pre-qualifying sessions at the last two Grands Prix, due to the withdrawal of the EuroBrun and Life teams. Pre-qualifying was necessary again in 1991 due to the arrival of two new entrants: Jordan and Modena, which were entirely new teams, running two cars each. Another new name, Fondmetal, was essentially a continuation of the defunct Osella team and was running a single car. Also involved in pre-qualifying were Coloni, running one car, and Scuderia Italia, running two cars. These were the two least successful surviving teams over the past two half seasons. The fastest four cars would go through to the main qualifying sessions.
Jordan had signed veteran Italian driver Andrea de Cesaris, plus last season's Coloni driver Bertrand Gachot, who had much experience in pre-qualifying sessions. Their car was the all-new 191 powered by a Cosworth V8 engine. Modena's drivers were Italian Nicola Larini, another driver well used to pre-qualifying, and Belgian debutant Eric van de Poele. They would be driving the Lamborghini V12-engined Lambo 291, so named for the team's strong Lamborghini connections. Coloni had brought the C4, a modified version of the C3 used in 1989 and 1990,
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Championship standings after the race
;Drivers' Championship standings
{| class="wikitable" style="font-size: 95%;"
|-
!Pos
!Driver
!Points
|-
|align="center"| 1
| Ayrton Senna
|align="right"| 10
|-
|align="center"| 2
| Alain Prost
|align="right"| 6
|-
|align="center"| 3
| Nelson Piquet
|align="right"| 4
|-
|align="center"| 4
| Stefano Modena
|align="right"| 3
|-
|align="center"| 5
| Satoru Nakajima
|align="right"| 2
|-
!colspan=4|Source:
|}
;Constructors' Championship standings
{|class="wikitable" style="font-size: 95%;"
|-
! Pos
! Constructor
! Points
|-
|align="center"| 1
| McLaren-Honda
|align="right"| 10
|-
|align="center"| 2
| Ferrari
|align="right"| 6
|-
|align="center"| 3
| Tyrrell-Honda
|align="right"| 5
|-
|align="center"| 4
| Benetton-Ford
|align="right"| 4
|-
|align="center"| 5
| Lola-Ford
|align="right"| 1
|-
!colspan=4|Source: