WASHINGTON - No, it's not over yet. But at this rate Mitt Romney's rivals won't catch him unless they pull off an unlikely fight at the Republican National Convention in August.

Romney is on a delegate-winning pace to secure the nomination in June, and at their current rate none of his GOP foes will reach even half the number needed.

The former Massachusetts governor's six victories on Super Tuesday netted him over 200 delegates to the party's convention - more than twice as many as any other candidate.

And to date, Romney has won 55 percent of the delegates at stake in primaries and caucuses.

At that pace, Romney won't reach the 1,144 delegates needed to clinch the Republican nomination until summer. That provides a lot of opportunities for slip-ups and intrigue - and plenty of incentive for Rick Santorum and Newt Gingrich to stay in the race and try to make up ground.

Romney's projecting confidence.

"We've got the time and the resources and a plan to get all the delegates, and we think that will get done before the convention," he said Wednesday on CNBC. Still, he also said he was "prepared to fight all the way" to the convention if needed.

The delegate math is worse for Santorum and Gingrich, despite Santorum's three victories on Tuesday.

At their current rate, they won't come close to catching Romney - unless something catastrophic happens to him. Their only hope is to stop Romney from reaching the victory threshold, then wrestle the nomination from him at the convention - a scenario that many GOP insiders see as far-fetched.

In the overall race for delegates, Romney leads with 419, including endorsements from Republican National Committee members who automatically attend the convention and can support any candidate they choose. Santorum has 178 delegates and Gingrich has 107. Texas Rep. Ron Paul trails with 47, according to the tally by The Associated Press.

Santorum has won 24 percent of the delegates in play so far, while Gingrich has won just 14 percent.

Santorum campaign spokesman Hogan Gidley acknowledges that Super Tuesday's results could feed a growing math problem for Santorum, but he also says the former Pennsylvania senator is determined to fight on.

"If we all go to the convention with a certain amount of delegates and we have to figure something out at the convention, then so be it," Gidley said. "But that's democracy and that's the way the party structure is set up. We'll cross that bridge when we come to it."

Romney has a 239-delegate lead on Santorum, which doesn't seem insurmountable. But it's hard to close a gap that size because of the way most states award Republican delegates.

Nearly every state uses some sort of proportional system to award delegates, so even losing candidates can win a significant number. That makes it difficult for Romney to amass enough delegates to claim the nomination, but it also makes it hard for Santorum and Gingrich to catch him.

In Oklahoma, for example, Santorum won the primary but got only one more delegate than Romney and Gingrich.

There are quirks in the rules, and Romney's campaign used them well in Tuesday's contests. In Massachusetts, Romney won all 38 delegates because no other candidate surpassed 15 percent of the vote, the minimum requirement to qualify for delegates.

In Virginia, Santorum and Gingrich failed to get on the ballot, and Romney won 43 of the state's 46 delegates. In Idaho, Romney's supporters mastered the state's complicated caucus system and ended up with all 32 delegates.

If the candidates keep winning delegates at their current pace, Romney's lead over Santorum would grow to more than 300 delegates by the end of March, and more than 400 by the end of April. Gingrich would be even farther behind, unless he can start winning states outside the South.

Nevertheless, neither Gingrich nor Santorum sound like they plan to leave the race.

"There are a lot of bunny rabbits to run through," Gingrich said, referring to the different candidates who have risen and fallen in the polls. "I'm the tortoise."

Santorum has tried to portray the race as a two-man contest, between Romney and him, hoping that he can solidify the anti-Romney vote behind him.

"We've won races all over this country against the odds. When they thought, oh, OK, he's finally finished, we keep coming back," Santorum told supporters. "We are in this thing."

Next up: Saturday caucuses in Kansas, the Virgin Islands, Guam and the Northern Mariana Islands. Wyoming also wraps up its county caucuses Saturday. Romney has support in Wyoming and the U.S. territories, though Kansas could be competitive.

Next Tuesday, the campaign heads south, for primaries in Alabama and Mississippi, where Romney has struggled. There are also caucuses in Hawaii and American Samoa.

"This is a very strange cycle, but none of it adds up to Rick Santorum being the nominee," said Rich Galen, a GOP strategist and former Gingrich aide who is neutral in the 2012 race. "Especially with Gingrich in the race siphoning off 25 percent of the conservative votes. There is no math that gets Santorum to 1,144."

Associated Press writer Steve Peoples contributed from Steubenville, Ohio.