The NASCAR O'Reilly Auto Parts Series (NOAPS) is a stock car racing series and NASCAR's second-highest national division, positioned between the Cup Series and the Truck Series, and typically runs as a support race the day before a Cup event. Originating from NASCAR's Sportsman division established in 1950, the modern series was formed in 1982 with Budweiser backing, and has since gone through several name changes—including Busch, Nationwide, and Xfinity—before becoming the O'Reilly Auto Parts Series starting in 2026. The series has evolved significantly, shrinking its starting grid from 43 cars to 36 (with a temporary bump to 40 during the COVID-19 pandemic) and introducing a seven-race Chase playoff format in 2016. It also celebrated a milestone on March 6, 2005, with its first race held outside the United States. Notably, sponsorship has shifted between major brands, with Comcast dropping the Xfinity sponsorship in 2025 to focus on the Cup Series, paving the way for O'Reilly Auto Parts to take over as title sponsor.