State Highway 99 (SH-99) is a north–south state highway through central Oklahoma. It runs from the Texas state line at Lake Texoma to the Kansas state line near Lake Hulah. It is 241.5 miles (388.7 km) long. The highway overlaps U.S. Highway 377 (US-377) for over half its length.

K-99 is a state highway in the U.S. state of Kansas. The highway runs 234.473 miles (377.348 km) from Oklahoma State Highway 99 (SH-99) at the Oklahoma state line near Chautauqua north to Nebraska Highway 99 (N-99) at the Nebraska state line in Summerfield. K-99 connects Emporia with several smaller county seats to the south and north, including Sedan, Howard, Eureka, Alma, and Westmoreland while passing through the Flint Hills of eastern Kansas.