The San Diego Chargers vs. The Oakland Raiders:

The San Diego Chargers' Biggest Rivalry has Probably been the Oakland Raiders.
These Two NFL Teams, The San Diego Chargers and the Oakland Raiders are both within the AFC West Division.
I have watched many SD Chargers and Raiders Games.
The San Diego Chargers currently have a 13 Game winning streak over the Oakland Raiders.
Here are the 13 straight Games in a row that the San Diego Chargers have won over the Oakland Raiders:

Sunday, December 28, 2003: Oakland Raiders at SD Chargers: Chargers Won: 21-14.

Sunday, October 31, 2004: Oakland Raiders at SD Chargers: Chargers Won: 42-14.

Sunday, November 21, 2004: SD Chargers at Oakland Raiders: Chargers Won: 23-17.

Sunday, October 16, 2005: SD Chargers at Oakland Raiders: Chargers Won: 27-14.

Sunday, December 04, 2005: Oakland Raiders at SD Chargers: Chargers Won: 34-10.

Monday, September 11, 2006: SD Chargers at Oakland Raiders: Chargers Won: 27-00.

Sunday, November 26, 2006: Oakland Raiders at SD Chargers: Chargers Won: 21-14.

Sunday, October 14, 2007: Oakland Raiders at SD Chargers: Chargers Won: 28-14.

Sunday, December 30. 2007: SD Chargers at Oakland Raiders: Chargers Won: 30-17.

Sunday, September 28, 2008: SD Chargers at Oakland Raiders: Chargers Won: 28-18.

Thursday, December 04, 2008: Oakland Raiders at SD Chargers: Chargers Won: 34-07.

Monday, September 14, 2009: SD Chargers at Oakland Raiders: Chargers Won: 24-20.

Sunday, November 01, 2009: Oakland Raiders at SD Chargers: Chargers Won: 24-16.