Mitt Romney and the Republicans raised $76.8 million, while the Obama campaign and the Democratic Party brought in $60 million.
Mitt Romney now has $107 million cash on hand, almost matching the $115 million Barack Obama’s campaign had by the end of April.
Barack Obama’s May total included $15 million raised at the home of George Clooney, with tickets costing $40,000.
Members of the public also bought $3 raffle tickets to win a spot at that star-studded event.
Both presidential candidates are in the midst of a hectic fund-raising schedule as they prepare for the long campaign ahead of November’s election.
Barack Obama is campaigning this week in California and Nevada, while Mitt Romney has been in Texas.
The monthly campaign fundraising totals do not include millions of dollars being raised and spent by independent committees backing each campaign.
May’s fundraising figures were the first since Mitt Romney became the official Republican nominee, having won the required numbers of delegates during the primary season to ensure he will face Barack Obama in November.
Announcing its fundraising totals early on Thursday, the Obama campaign said on Twitter that 572,000 people donated in May, 147,000 of them for the first time.
His campaign also reported that 98% of the contributions were less than $250.
In its statement shortly afterwards, the Romney campaign reported that donations of $250 or less made up 93% of all donations and $12 million of the total amount raised.
“Our strong fundraising is a sign that Americans are tired of President Obama’s broken promises and want a change of direction in the White House,” Republican National Committee Chairman Reince Priebus said in a statement.
Barack Obama campaign spokesman Ben LaBolt used Twitter to play down Mitt Romney’s fundraising haul: “Reminder on RNC/Romney camp fundraising: 1st month joint committee was in existence, so all their primary donors wrote their maxout checks.”
Both the camps raised considerably more in May than in April, when the Obama campaign and the Democrats brought in $43.6 million, slightly ahead of their opponents.
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