The 1991 Daytona 500 By STP was the first stock car race of the 1991 NASCAR Winston Cup Series season and the 33rd iteration of the event.

Following a period of three late-race cautions, Morgan–McClure Motorsports driver Ernie Irvan took the lead from Dale Earnhardt with six laps left in the race.

Teams considered it too time-consuming to change four tires since it had to be done under green (at the time, a four-tire pit stop would take roughly 20–25 seconds).

For an example of how the rules adversely affected the racing, Kyle Petty ran the entire 500 miles on the same left side tires.

Bill Elliott suffered a flat tire early on, and was forced to limp around the track at a reduced pace for two laps before he was allowed to pit, effectively eliminating him from the competition.

The pits were closed at the onset of caution, then opened after the pace car had picked up the leader and the field was sufficiently "packed-up" (that usually took one lap).

The pit road speed limit and use of the "lollipop" style signboard were the significant changes made permanent (and remain to this day).

Drivers would be required to gauge their own pit lane speed (by monitoring their RPMs) and officials enforced the infractions with a system similar to VASCAR.

Davey Allison, driving for Robert Yates Racing, won the pole with a time of 45.929 and an average speed of 195.955 miles per hour (315.359 km/h) in Saturday's session.

Meanwhile, turn 4 was coated with oil, gathering Jeff Purvis, Jimmy Means, Phil Barkdoll, and again Sammy Swindell.

The windshield slid across the track and into Ken Schrader's bumper and air dam, puncturing the radiator and causing a lengthy repair that eliminated the three-time Daytona 500 polesitter from contention.

1990 Winston Cup runner-up Mark Martin moved through the field quickly in the early going, but was also eliminated from contention as the center section of the car's rear gearing sheared completely off of the driveshaft, causing him to spend many laps behind the wall.

The lead changed hands many times, as Dale Earnhardt, Joe Ruttman, Davey Allison, Sterling Marlin, Rick Mast, Kyle Petty, Ernie Irvan, and Darrell Waltrip had all pitted on varying laps.

He was quickly shuffled off of the lead on the restart, and was touched by Kyle Petty in Turn 4, which broke the car loose and sent him into a spin.