Up to six months ahead of actual production, U.S. automakers announce plans for their monthly domestic production of cars. A leading industry trade journal publishes the initial plans and then a series of revisions leading up to the month in question. We analyze a panel data set spanning the years 1965–95, matching the production forecasts with data for actual monthly production. We show that a firm's plan announcement affects competitors' later revisions of their own plans and eventual production. The interaction appears to be complementary: large plans or upward revisions cause competitors to revise plans upward and increase production. The results are consistent with theoretical models in which firms share information about common demand parameters.