U.S. Route 20 in Oregon is a major east–west cross-state highway, especially east of the Cascade Mountains. It connects U.S. Route 101 in Newport on the central Oregon Coast to the Idaho state line east of Nyssa.

U.S. Route 20 in Oregon begins at an intersection with U.S. 101 in Newport, and runs eastward over the Central Oregon Coast Range to Corvallis. In Corvallis, it intersects Oregon Route 99W and briefly overlaps Oregon Route 34 before proceeding northeast to Albany. From Albany, U.S. 20 briefly overlaps Oregon Route 99E before turning east through Lebanon and Sweet Home and entering the Cascade Mountains. It intersects Oregon Route 126 west of Santiam Pass and the two routes overlap through Sisters. U.S. 20 then continues eastward and southward to Bend, where it overlaps U.S. 97 for about 5 miles (8.0 km) before turning east through Brothers and Riley. At Riley, U.S. 20 overlaps U.S. 395 through Hines and Burns to about 2 miles (3.2 km) northeast of Burns. From Burns, U.S. 20 continues east through Juntura and Vale. In Vale, U.S. 20 overlaps U.S. 26, and the two highways continue east to Cairo Junction, south of Ontario, and turn south, where they then also run concurrently with Oregon Route 201 to Nyssa. Eastward from Nyssa, U.S. 20 and U.S. 26 continue to the Idaho border.

U.S. Route 20 has 2 business routes in Oregon: one in Toledo, and one in Bend.

Construction on a portion of U.S. 20 between Newport and Corvallis, specifically, near Toledo to Eddyville, is being done to straighten and remove nearly three miles from the route, and make it easier for larger vehicles to travel. Construction began in 2005, but was halted in 2007 because of excessive unexpected landslides. The project recommenced in May 2008 with a better plan for stabilizing these landslide locations. The final construction was expected to be completed in 2011, but continuing earth movement at a bridge site has delayed the project again. ODOT and the contractor were in a dispute over liability and money, a settlement was agreed upon, and the original build contract has been rescinded. A new contractor is now on the job and because of the previous delays the completion date of the project has been postponed until fall of 2015.

The Oregon section of U.S. 20 consists of the following highways (see Oregon highways and routes), from west to east: