Entering the general election campaign with a slight lead on McCain in public opinion polls, Obama sought to exploit Americans' anxiety over high fuel prices on Monday.
He said he would impose a windfall profits tax on US oil companies if he was elected.
He drew a sharp contrast with McCain, accusing him of wanting to widen tax cuts introduced by the current president, George Bush, and send the US deeper into debt.
"If John McCain's policies were implemented, they would add $5.7 trillion to the national debt over the next decade. That isn't fiscal conservatism, that's what George Bush has done over the last eight years," Obama told a crowd in the town of Raleigh in the state of North Carolina.
Obama opened his economic tour in a state that Bush won in 2004 with 56 per cent of the vote.
Obama won the state's Democratic contest by a wide margin over Hillary Clinton.
"You don't have to read the stock tickers or scan the headlines in the financial section to understand the seriousness of the situation we're in right now."
Earlier Bush himself commented on the weak dollar and rising oil prices before leaving for his last tour of Europe as president.
He reiterated his stance that the US should increase domestic oil production and that congress should allow drilling in Alaska's Arctic National Wildlife Refuge.
"We'll remind our friends and allies overseas that we are all too dependant on hydrocarbons and we must work to advance the technologies that help us become less dependant on hydrocarbons," Bush said on Monday.
"Our capital markets are some of the deepest and most liquid and the longterm health, strong foundation of our economy will shine through and be reflected in currency values. The US economy's continuing to grow in the face of unprecedented challenges."
Despite Bush's upbeat economic analysis Al Jazeera's senior Washington correspondent Rob Reynolds says that there are two alternate realities in the US economy today.
"On the one hand there are Americans who are really struggling even to find money for food while President Bush is talking of the liquidity of markets and that has created some anger among the public.
|McCain has repeatedly accused Obama of|
being too inexperienced to lead the US [AFP]
"And that is something Obama is trying to tap into and is trying to tie McCain to all that has gone before."
With Americans struggling to pay for record high $4-a-gallon petrol, unemployment up and consumer confidence down, Obama is attempting to focus the general election campaign on the economy.
The economy is more familiar territory for Obama whereas the more experienced McCain has used national security and foreign policy as the centerpiece for his campaign.
McCain has repeatedly accused Obama of being too inexperienced to lead the country.
Obama renewed his call for a $50bn stimulus package as a way to try to spur consumer spending and jolt new life into the economy, and a $10bn fund for homeowners caught up in the housing crisis.
"I'll make oil companies like Exxon pay a tax on their windfall profits, and we'll use the money to help families pay for their skyrocketing energy costs and other bills," he said.
Obama, 46, the Illinois senator who is hoping to be America's first black president, charged that McCain's support for extending Bush's tax cuts would allow $2 trillion in corporate tax breaks, including $1.2bn for Exxon Mobil Corp, which had earnings last year of $40.61bn.
McCain, 71, the Arizona senator who would be the oldest candidate ever elected to a first US presidential term, raised campaign funds in the state of Virginia on Monday and reminded his audience about his challenge to Obama to join him in 10 face-to-face town hall meetings to debate the issues.
He had offered the first face-off to take place on Thursday at New York's Federal Hall.