Obama told a town-hall meeting the rebate would be financed with a windfall profits tax on the oil industry.
"This rebate will be enough to offset the increased cost of gas for a working family over the next four months," Obama said in the crucial swing state of Florida.
Obama had earlier said the rebates should be part of a larger tax relief package. But now he says the slumping economy demands they be put in place immediately.
Obama's remarks coincide with news that the unemployment rate climbed to a four-year high of 5.7 percent in July as employers cut 51,000 jobs, dashing the hopes of an influx of young people looking for summer work. Payroll cuts weren't as deep as the 72,000 predicted by economists, however. And, job losses for both May and June were smaller than previously reported.
July's reductions marked the seventh straight month where employers eliminated jobs. The economy has lost a total of 463,000 jobs so far this year.
"We can either choose a new direction for our economy, or we can keep doing what we've been doing," Obama said.
During his speech, Obama was interrupted by three men who stood up with a banner asking, "What about the black community, Obama?" Many in the crowd began chanting, "Yes, we can," the Obama campaign mantra to counter the criticism.
Obama told the three that they would have a chance to ask questions after he had his opportunity to speak. A town-hall organizer later took the banner from the three.
During a question and answer session, Obama called on one of the hecklers, reports CBS News' Michelle Levi.
The man mentioned a slew of controversial issues, such as the government's response to Hurricane Katrina and the subprime mortgage crisis and asked, "In the face of all these attacks that are clearly being made on the African community, why is it that you have not had the ability to not one time speak to the interests and even speak on the behalf of the oppressed and exploited African community or Black community in this country?"
"I think you are misinformed about when you say, 'not one time,'" Obama responded. "Every issue you've spoken about, I actually did speak out about."
The Illinois senator then went on to address the man's concerns, mentioning that he was a civil rights lawyer and saying, "I may not have spoken out the way you would have wanted me to speak out, which is fine."