Here's the top 50 as of the end of 2005: Which also includes when they were in Philadelphia (1901-1954) and Kansas City (1955-1967). OAKLAND A'S SEASON HOMERUNS YEAR HR 1 Jimmie Foxx 1932 58 2 Mark McGwire 1996 52 3 Mark McGwire 1987 49 4 Jimmie Foxx 1933 48 5 Reggie Jackson 1969 47 T6 Jimmie Foxx 1934 44 T6 Jose Canseco 1991 44 8 Jason Giambi 2000 43 T9 Jose Canseco 1988 42 T9 Mark McGwire 1992 42 T9 Gus Zernial 1953 42 T12 Mark McGwire 1995 39 T12 Mark McGwire 1990 39 T14 Bob Cerv 1958 38 T14 Jason Giambi 2001 38 T14 Matt Stairs 1999 38 T17 Tilly Walker 1922 37 T17 Jimmie Foxx 1930 37 T17 Jose Canseco 1990 37 T20 Al Simmons 1930 36 T20 Reggie Jackson 1975 36 T20 Geronimo Berroa 1996 36 T20 Jimmie Foxx 1935 36 T24 Tony Armas 1980 35 T24 Dave Kingman 1984 35 T24 Terry Steinbach 1996 35 T24 John Jaha 1999 35 T24 Dave Kingman 1986 35 T24 Al Simmons 1932 35 T30 Bob Johnson 1934 34 T30 Eric Chavez 2002 34 T30 Mark McGwire 1997 34 T30 Al Simmons 1929 34 T30 Rocky Colavito 1964 34 T30 Miguel Tejada 2002 34 T36 Dwayne Murphy 1984 33 T36 Jimmie Foxx 1929 33 T36 Mark McGwire 1989 33 T36 Jason Giambi 1999 33 T36 Gus Zernial 1951 33 T36 Jose Canseco 1986 33 T42 Reggie Jackson 1973 32 T42 Mark McGwire 1988 32 T42 Reggie Jackson 1971 32 T42 Eric Chavez 2001 32 T46 Miguel Tejada 2001 31 T46 Bob Johnson 1940 31 T46 Sal Bando 1969 31 T46 Jose Canseco 1987 31 T50 Bob Johnson 1938 30 T50 Jimmie Foxx 1931 30 T50 Dave Kingman 1985 30 T50 Gus Zernial 1955 30 T50 Miguel Tejada 2000 30