The online sales tax loophole is costing Massachusetts $387 million in state tax revenue, $280 million in sales to local businesses, and nearly 2,000 jobs, according to a new economic study released on Tuesday by the Massachusetts Main Street Fairness Coalition.

The report, prepared by Cape Ann Economics, examined $6 billion in online purchases made by Massachusetts consumers in 2011. The study determined that the state lost $387 million in state tax revenue in 2011 and projected that figure would roughly double to $783 million in 2020.