Worldwide, Whitney Houston has the best selling single by a solo female artist with I Will Always Love You, but Cher did better than her on chart performance with her song Believe.
I think here in the United States, We Belong Together sold more than I Will Always Love because the Internet wasn't available way back in 1992.
vrfkdcp, your words lingered in my head, and I checked with Wikipedia again for some facts, and interestingly, this is what I got from several pages of Wikipedia.
Worldwide Alleged Sales
http://en.wikipedia.org/wiki/List_of_best-selling_singles_worldwide
At least 10 million copies
Celine Dion - My Heart Will Go On 1997
Cher - Believe 1998
Madonna - Hung Up 2005
Patti Page - Tennessee Waltz 1950
(Shakira feat Wyclef Jean - Hips Don't Lie 2006)
Whitney Houston - I Will Always Love You 1992
At least 5 million copies
Avril Lavigne - Complicated 2002
Britney Spears - ...Baby One More Time 1999
Britney Spears - Oops!...I Did It Again 2000
Britney Spears - Toxic 2004
Cher - The Shoop Shoop Song (It's in His Kiss) 1990
Cher - Strong Enough 1999
Debbie Boone - You Light Up My Life 1977
Gwen Stefani - The Sweet Escape 2007
Janet Jackson - Together Again 1997
Jeannie C. Riley - Harper Valley PTA 1968
Julie Rogers - The Wedding 1964
Kylie Minogue - Can't Get You Out Of My Head 2001
Madonna - Music 2000
Madonna - Vogue 1990
Madonna - American Pie
Madonna - Sorry 2005
Mariah Carey - We Belong Together 2005
Mary Hopkin - Those Were the Days 1968
Nelly Furtado - Say It Right 2007
(Rihanna feat Jay-Z - Umbrella 2007)
Shakira - Whenever, Wherever 2001
Utada Hikaru - Flavor of Life 2007
Sales in the USA only
http://en.wikipedia.org/wiki/List_of_best_selling_singles_(USA)
Over 4 million:
* "I Will Always Love You", Whitney Houston
* "I Think We're Alone Now", Tiffany
Over 2 million:
* "...Baby One More Time", Britney Spears
* "Bad Girls", Donna Summer
* "Believe", Cher
* "Emotion", Samantha Sang
* "Fantasy", Mariah Carey
* "Hot Stuff", Donna Summer
* "I Will Survive", Gloria Gaynor
* "If Your Girl Only Knew", Aaliyah
* "Knock On Wood", Amii Stewart
* "Mickey", Toni Basil
* "Mr Big Stuff", Jean Knight
* "Nobody's Supposed to Be Here", Deborah Cox
* "Vogue", Madonna
* "You Light Up My Life", Debby Boone
If anyone should need reference, they are in those sites. Interestingly, and I was surprised to know that Madonna did score ok with her singles from Confessions. And to know that Tiffany shared the glamor with Whitney Houston in the USA for sales over 4 million copies. Like wow.
I added Shakira and Rihanna's singles, although they are not solo efforts.
