New analysis of oil industry contributions to members of Congress has revealed the level of the oil lobby's financial firepower that Barack Obama can expect to face in the November elections if he refuses to approve the Keystone XL tar sands pipeline.

Obama has until February 21 to make a decision on whether to approve the pipeline, under a compromise tax measure approved late last year. America's top oil lobbyist warned last week that the president would face "huge political consequences" if he did not sign off on the project to pump tar sands crude across the American heartland to refineries on the Texas coast.

The Canadian government is also on the offensive, with an attack this week on "jet-setting celebrities" opposed to tar sands pipelines. At the same time, TransCanada executives have embarked on a letter-writing campaign.

Now Maplight, an independent research group in Berkeley, California, that tracks the influence of money in politics, has conducted an analysis of oil industry contributions to members of Congress supporting the pipeline.

The study, which is due to be published on Wednesday, studied industry contributions to members of the House of Representatives which passed a bill last July that would have forced Obama to speed up approval of the Keystone project.