What percentage of US Marines are gay?

6.4%

there are approximately 12,951 women in the marine corps out of 202,786 or 6.4%, with another 5,334 women in the marine corps reserve out of 95,199 or 5.6%.

if you combine the two numbers there are 18,285 female marines out of 297,985 or 6.1%

these statistics are accurate as of Sept 30, 2009 and courtesy of the Department of Defense.