Barack Obama has laid out an ambitious energy plan under which US dependence on foreign oil would end within 10 years.
The Democrat contender's policy is seen as an attempt to blunt the apparent progress his Republican opponent John McCain is making with US voters who are struggling with high energy costs.
During a speech in Lansing, Michigan, Mr Obama performed a U-turn by calling for the release of 70 million barrels of crude oil held in federal stockpiles as a short-term means of lowering gasoline prices.
Last week, the Illinois senator also changed his position on his opposition to ending a quarter-century ban on drilling for oil along America's coast. He said he could accept limited and environmentally sound offshore exploration as part of a larger energy compromise that was being formulated in Congress.
The struggling US economy and rocketing energy costs are top of voter concerns, and Mr McCain has made headway in the White House contest by calling for an end to the drilling ban.
Mr McCain's campaign team described Mr Obama's policy switch yesterday as a "flip-flop".