In Pixar's Cars, the fictional fuel brand that sponsors Lightning McQueen is Rust-eze.
Rust-eze is an automotive product brand marketed as a remedy for rusty bumpers. Its orange-and-yellow logo appears on McQueen's body and race equipment. The sponsorship is a major part of his early professional identity and helps establish him as a rookie racer rather than an already established champion.
Rust-eze is associated with brothers Rusty and Dusty Rust-eze, who discover McQueen and support his career. McQueen initially views the sponsorship as less prestigious than the Dinoco brand, which represents a more glamorous racing opportunity. That tension helps drive his desire to win the Piston Cup.
Dinoco and Rust-eze are separate fictional brands. Confusing them is common because Dinoco is highly visible in the racing storyline and later becomes connected to McQueen's career. Rust-eze, however, is the sponsor displayed on McQueen at the start of the original film.