Insurers and policy makers have created health care price transparency websites to facilitate price shopping and reduce spending. However, price transparency tools to date have been plagued by low use. It is unclear whether this low use reflects a lack of interest or a lack of awareness. We launched a large online advertising campaign to increase consumers' awareness about insurer-specific negotiated price information available on New Hampshire's public price transparency website. Our campaign led to a more than 600 percent increase in visits to the website. However, in our analysis of health plan claims, this increased use of the website did not translate to increased use of lower-price providers. Our findings imply that the limited success to date of price transparency tools in reducing health care spending is driven by structural factors that limit consumers' ability to use health care price information as opposed to only a lack of awareness about price transparency tools.