The 2008 General Social Survey involved face-to-face interviews with about 2,000 adults (though nearly 13% declined to answer the questions about sexual orientation and behavior). According to an analysis of the data by The Williams Institute, less than 2% of men said they were gay, less than 2% of women said they were lesbian, and less than 2% altogether identified as bisexual. But another 6%, who consider themselves straight, reported having had sex with someone of the same sex. In total, nearly 10% could be considered something other than heterosexual based on self-identification or sexual history.
Of note, women were twice as likely as men to consider themselves bisexual, while men were twice as likely to consider themselves straight even when they had had a same sex partner. This may reflect greater stigma for men in being anything other than straight.
The National Survey of Sexual Health and Behavior of 2009 focused more on specific sexual behaviors and was conducted over the internet, which may have been less embarrassing. Nearly 6,000 adolescents and adults agreed to participate. According to the special issue of the Journal of Sexual Medicine which published the results, about 8% of adults consider themselves something other than straight, with women much more likely to identify as bisexual or “other.” The highest rate of bisexual identification (8.4%) was reported by adolescent girls (who were also much more likely than boys to engage in same-sex behaviors).
The published findings regarding sexual behaviors are frustratingly incomplete, in that they do not distinguish whether insertive anal practices and mutual masturbation were conducted with same-sex or opposite-sex partners, and cunnilingus seems to be the only same-sex activity identified for women. That said, the following rates of same-sex behavior were found among adult men: 8-15% have received oral sex, 6-13% have given oral sex, and 4-11% have received anal sex. Among women, 4-17% have received oral sex from a woman, and 4-14% have given oral sex to a woman. (The ranges reflect the rates in different age groups.)
Again, the rates of same-sex behavior are considerably higher than the rates of gay and bisexual identification, which confirms previous findings that most men and women who have had homosexual experiences nevertheless consider themselves straight (in my schema, most would probably be heteroflexible).
Of note, neither of these surveys sampled institutional settings, such as dormitories, barracks, and jails, where same-sex behavior may be more common. If we were to add in those settings and consider any same-sex behaviors that lead to orgasm, rates of de facto bisexuality would probably be closer to the 20-30% originally identified by Kinsey.