Moreover, laws against marijuana possession are so widely flouted that enforcement has to be highly selective, usually with disturbing results. Although white and black Americans report using marijuana at similar rates, African Americans accounted for 82 percent of the Philadelphians arrested for pot possession in 2010, according to a study by the American Civil Liberties Union. And such disparities appear to be growing, the ACLU found: From 2001 to 2010, black Philadelphians went from being twice as likely to being nearly five times as likely as whites to be arrested for possessing marijuana.