What is the most played college basketball rivalry?

The most contested rivalry in division I men's basketball is between Oregon State University and the University of Oregon. It was played 331 times before the conclusion of the 2009 season.

The series has been played so often because of the close proximity of the campuses (45 miles), the relative isolation from other potential opponents in the days before long distance travel was common, and the long histories of each program (they first played one another in 1903). In fact, the six most played series in college basketball are all contests between Pacific Northwest schools:

1. Oregon State vs. Oregon, 331 games

2. Oregon vs. Washington, 284 games

3. Oregon State vs. Washington, 283 games

4. Oregon State. vs. Washington State, 278 games

5. Oregon vs. Washington State, 276 games

6. Washington vs. Washington State, 267 games

7. Kansas vs. Kansas State, 266 games

Source: NCAA Division I Men's basketball records.