WTA Tier I tournaments

The WTA Tier I tournaments were Women's Tennis Association tennis elite tournaments held from 1990 until the end of the 2008 season. From 1988 to 1990, the different levels of WTA tournaments were referred to by the term 'Category', and there were 5 categories. Two of the Tier I tournaments, Indian Wells and Miami, were also joint events held simultaneously with the ATP Tour Masters Series.
There were initially 6 Tier I tournaments held annually from 1990. The list expanded to 8 events in 1993, 9 in 1997 and 10 in 2004, before being scaled back to 9 for 2008.
In 2009 the WTA changed the tournament categories, so that the majority of Tier I and Tier II tournaments were in one category, Premier Tournaments, split into three categories.
Tier I records & statistics.
Singles.
Tokyo—Miami—Canada—Zurich ("The Hard Quadruple") Hingis, 2000
Indian Wells—Miami—Canada ("The Hard Triple") Clijsters, 2005
Indian Wells—San Diego—Zurich ("The Hard Triple") Sharapova, 2006
A number of players hold records for winning the tournaments multiple times, while other records are achieved for successive tournament wins, mini-combination victories amongst others.