15 in 2001
The Seattle Mariners lost 14 games in a row from 9-2-1992 to 9-18-1992; their longest losing streak as of 7-20-2011.
Ken Griffey Jr.
In 2008, the longest winning streak for the Seattle Mariners was four games. It ran from August 29th through September 1st.
Pete Rose had a 44 game hitting streak in 1978.
George Brett had a 30-game hitting streak.
30 by Willy Taveras in 2006
35 by Luis Castillo in 2002
31 by Vladimir Guerrero in 1999