Greenwashing works — that’s one interpretation of a recent working paper from the National Bureau of Research examining the impact of advertising on oil company BP. In the paper, economists from the University of Maryland, University of Michigan, and Brown set out to measure the influence of BP’s pre-spill green advertising campaign on the company’s performance following the 2010 Deepwater Horizon oil spill. Using gas prices, sales, and station affiliations, as well as data on BP’s ad spending, the researchers reach a troubling conclusion: consumers did “punish” BP temporarily following the spill, but that punishment “was significantly reduced by pre-spill exposure to BP advertising during the ‘Beyond Petroleum’ campaign years.” In other words, green advertising functioned as an insurance policy against the cost of an environmental disaster.