The European Union says crude oil extracted from Alberta’s tar sands should be ranked as a dirtier fuel source than oil tapped from conventional oil wells, a move that could effectively ban the import of the controversial oil. The European Commission endorsed a measure that would essentially rate fossil fuels based on the CO2 emited during extraction, refining, and combustion. The EU has proposed that tar sands oil be ascribed a greenhouse gas value of 107 grams per megajoule of fuel, compared with 87.5 grams for ordinary crude oil. “With this measure, we are sending a clear signal to fossil fuel suppliers,” said Connie Hedegaard, the EU’s climate change commissioner. “As fossil fuels will be a reality in the foreseeable future, it’s important to give them the right value.” Such a ratings system may eventually be applied to natural gas extracted from shale oil formations. The exploitation of Alberta’s tar sands has generated increasing protest from environmental groups. In addition to destroying large swaths of forest, the extraction and processing of the sludgy bituminous material typically requires more energy and water than conventional production.