NASCAR's second national division was known as the Busch Grand National Series from 1984, became the Busch Series in 2003, and transitioned to the Nationwide Series in 2008 when Nationwide Insurance assumed title sponsorship on a reported ten-million-dollar initial commitment for that year, with six-percent annual escalations thereafter. The Nationwide sponsorship was structured as a seven-year contract.
On September 3, 2014, NASCAR and Comcast announced that the consumer cable and wireless brand Xfinity would become the new title sponsor of the series. The series was renamed the NASCAR Xfinity Series beginning with the 2015 season.
Under the Xfinity name, the series continued its role as NASCAR's primary developmental division, positioned between the Cup Series and the Craftsman Truck Series. The series maintained a field size that shifted over the years, beginning with up to 43 cars per race before progressively reducing to 40 cars in 2013, then to 38 in 2019 and 36 in 2020.
In 2016, NASCAR introduced a Chase playoff format to the Xfinity Series, mirroring the championship structure adopted by the Cup Series in 2004. The format consisted of seven races with a field of drivers competing through multiple rounds.
The debate over "Buschwhacking" — Cup Series drivers competing in the lower series and displacing developmental racers — remained a background tension throughout the Xfinity era. From 2017 onward, NASCAR limited Cup drivers with at least five years of Cup experience to a maximum of ten Xfinity races per season, and barred them from the series' playoff and Dash 4 Cash races.
The Xfinity Series also returned to international racing during this period. In 2025, the series raced at Autódromo Hermanos Rodríguez in Mexico City, where Mexican driver Daniel Suárez won the race.
In February 2025, Comcast renewed its broader sponsorship relationship with NASCAR but elected not to continue the Xfinity Series title sponsorship beyond the 2025 season. The company chose instead to concentrate its NASCAR investment on Xfinity's role as a Premier Partner of the Cup Series and to sponsor a newly introduced fastest lap award across all three national series. On August 18, 2025, NASCAR announced that O'Reilly Auto Parts would assume title sponsorship of the series beginning with the 2026 season, and the series was renamed the NASCAR O'Reilly Auto Parts Series.
The eleven-year Xfinity sponsorship of NASCAR's second-tier series was the longest by a single brand in that division's history since the Busch/Anheuser-Busch arrangement. It established the series's identity during a period of significant structural change in NASCAR broadcasting, including the series's move to FS1 and subsequently to The CW. The "Xfinity Series" name became firmly associated with the sport's developmental pipeline, and the Xfinity brand gained extensive motorsport visibility across a period when cord-cutting was reshaping the cable industry.