Big Law is not known as a welcoming place for women partners. But a close look at the latest numbers reveals that women are actually making gains—sometimes substantial gains—at many of the über-elite Am Law 200 firms. In the race for equity partnership—the coveted prize of Big Law—female lawyers at firms with a one-tier partnership are outpacing their sisters at firms with two-tier partnerships. The difference is only a few percentage points, but it is striking: In the Am Law 200 pool, women at single-tier firms (where all partners have equity) currently hold 17.9 percent of the partnership; at two-tier firms—composed of equity and nonequity/income partners—women constitute just 14.6 percent of the equity partners, but 24.6 percent of nonequity partners. [For a chart showing the ratio of women partners at one-tier Am Law 200 firms, see "One Singular Sensation."]

The numbers tell the story: Of the 30 one-tier firms (out of 31) on the 2012 Am Law 200 list that provided a gender breakdown, 22 boast female equity partnership rates above 15 percent. (The American Lawyer defines equity partners as “those who receive no more than half of their compensation on a fixed-income basis.”) Those 22 firms include some of the most profitable, bluest of the blue chips, in the industry, such as Wilmer Cutler Pickering Hale and Dorr (23.2 percent women equity partners); Ropes & Gray (20.7 percent); Davis Polk & Wardwell (20.3 percent); Arnold & Porter (19.5 percent); and Munger, Tolles & Olson (19 percent).