Óscar Eduardo Villarreal (Spanish pronunciation: [ˈoskaɾ βiʎareˈal]; born November 22, 1981) is a Mexican former professional baseball pitcher.

Villarreal played the entire 2001 season with the Double-A El Paso Diablos, where he logged a 6–9 record with a 4.41 ERA and 108 strikeouts.

He finished second in the league in games pitched to Paul Quantrill, and also tied Brandon Webb's Diamondbacks record for wins by a rookie.

However, on June 5, Villarreal suffered an injury when a line drive off the bat of Frank Thomas hit him in the shin.

After playing on a rehab assignment with the Tucson Sidewinders in July, doctors took an MRI on Villarreal's elbow on August 6 and determined that he would need to undergo season-ending nerve transposition surgery.

On December 7, 2005, Villarreal and fellow pitcher Lance Cormier were traded to the Atlanta Braves for catcher Johnny Estrada.

He signed a minor league contract with the Seattle Mariners and was assigned to their Triple-A affiliate, the Tacoma Rainiers, on July 22, 2008.

After missing all of 2009 due to Tommy John surgery, he signed on February 4, 2010, a Minor League contract with the Philadelphia Phillies.

On November 23, 2010, he signed a minor league contract with the Los Angeles Dodgers, that included an invitation to spring training.

[5] He began the season in AAA with the Albuquerque Isotopes but on April 11, he was loaned to the Sultanes de Monterrey of the Mexican League.

[6] Late in 2012, he signed a minor league contract with the Boston Red Sox with spring training invitation and was assigned to AAA Pawtucket.