The 78th Indianapolis 500 was held at the Indianapolis Motor Speedway in Speedway, Indiana on Sunday, May 29, 1994. Al Unser, Jr. won from the pole position, his second Indy 500 victory. Much to the surprise of competitors, media, and fans, Marlboro Team Penske arrived at the Speedway with a brand new, secretly-built 209 in³ (3.42 L) displacement Mercedes-Benz pushrod engine, which was capable of nearly 1,000 horsepower (750 kW). Despite reliability issues with the engine and handling difficulties with the chassis, the three-car Penske team (Unser, Emerson Fittipaldi and Paul Tracy) dominated most of the month, and practically the entire race.

Though Al Unser, Jr. won the pole position, it was Emerson Fittipaldi who dominated most of the race, leading a total of 145 laps. On lap 185, Fittipaldi was leading the race, and was looking to put Unser, Jr. (who was running second) a lap down. Fittipaldi was in reach of his second-consecutive Indy 500 victory, and third overall. Shockingly, Fittipaldi tagged the wall in turn 4, handing the lead to Unser, Jr. with 15 laps to go. Little Al was able to stretch his fuel and cruise to victory over rookie Jacques Villeneuve. Al Unser, Jr. joined his father Al Sr. and uncle Bobby as winners of multiple 500s at Indy.

The race marked the final Indy 500 for Mario Andretti, who retired after the 1994 season. Indy veterans Al Unser, Sr. and Johnny Rutherford also retired in the days leading up to the race. John Andretti, who had left CART and moved to the NASCAR Winston Cup Series, became the first driver to race in both the Indy 500 and Coca-Cola 600 in the same day, an effort that has become known as "Double Duty." This was also the second and final Indy 500 for Nigel Mansell, who was knocked out of the race in a bizarre crash with Dennis Vitolo. It was not known at the time, but when Emerson Fittipaldi hit the wall on lap 185, it would conclude his final competitive lap in the Indy 500; he did not qualify for the 1995 race and the 1996 race was boycotted by CART.

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