WASHINGTON -- The Natural Resources Defense Council on Tuesday released a report dispelling the myth that the proposed Keystone XL tar sands pipeline would lower gas prices. Rather, the opposite is true, findings show.

On a conference call with reporters on Tuesday, report author and NRDC attorney Anthony Swift called the pipeline's impact on gasoline prices "one of the most misunderstood issues surrounding the proposed Keystone XL," adding that when TransCanada originally proposed the pipeline, they pitched it as a way to increase the cost of oil in the United States, providing increased revenue for Canadian producers. Since then, proponents of the pipeline in the United States have pitched it as a means of decreasing U.S. gasoline prices.

Swift's study examined these two conflicting claims, and findings suggest that the former is the true one. "Our study has found that Keystone XL is likely to both decrease the amount of gasoline in U.S. refineries for domestic markets and increase the cost of producing it, leading to even higher prices at the pump," Swift told reporters.

TransCanada did not immediately return a request for comment.

The report found the pipeline will increase U.S. gasoline prices by three mechanisms, most immediately by reducing the amount of gasoline produced in the United States. The pipeline will divert crude oil from Midwestern refineries, which are designed to produce as much gasoline as possible from a barrel of oil, to Texas Gulf refineries, which are designed to produce as much diesel as possible from a barrel of oil. The result in the immediate to short term will be a decline in gasoline production and an increase in diesel, according to the report.

Other findings in the report include that the pipeline will increase the price of crude oil in the Midwest and Rocky Mountains by over $20 a barrel, increasing the cost of Canadian tar sands by as much as $27 billion annually. These higher crude oil costs are expected to lead to deteriorating financial conditions in Rocky Mountain and Midwestern refineries, which could in turn result in decreased production. That's because if Midwestern refineries are forced to pay a higher price for oil, as East Coast refineries already do, they will be forced to respond by reducing their production and further decreasing U.S. gasoline supplies, according to the report.

These findings come as the House and Senate are in conference to hammer out a final version of the transportation bill. A provision in the House version of the bill would approve the pipeline, overriding President Obama’s rejection of the pipeline application in January, but a similar provision has not, as yet, been included in the Senate's version. The president has promised to veto any measure that includes Keystone XL approval.