Previous investigations into the impact of open-access journals on subsequent citations confounded open and electronic access and failed to track availability over time. With new data, we separated these effects. We demonstrate that a journal receives a modest increase in citations when it comes online freely, but the jump is larger when it first comes online through commercial sources. This effect reverses for poor countries where free-access articles are much more likely to be cited. Together, findings suggest that free Internet access widens the circle of those who read and make use of scientists' investigations.