Sen. Barack Obama rolled up an easy victory Tuesday in the Mississippi primary, gaining steam ahead of next month's big Democratic showdown in Pennsylvania.

The results reflected a stark racial divide; more than 9 in 10 blacks voted for Obama, while Sen. Hillary Rodham Clinton won the votes of 7 in 10 whites, according to exit polls. Black voters accounted for roughly half the turnout.

Speaking from Chicago, Obama said he was grateful to the people of Mississippi for his strong showing. "It's just another win in our column and we are getting more delegates," he said in an interview with CNN.

In a statement, Clinton campaign manager Maggie Williams congratulated Obama on his win. "Now we look forward to campaigning in Pennsylvania and around the country as this campaign continues," she said.

The Republican primary held little mystery. Sen. John McCain of Arizona, who has amassed enough delegates to win his party's nomination, won as expected. On Tuesday, he was in New York, attending an evening fundraiser that was expected to raise $1 million.

The victory Tuesday was Obama's second straight — after winning Saturday's Wyoming caucuses — continuing the primary-state back-and-forth with Clinton, who won three of the four contests a week ago, including Ohio and Texas.

The next six weeks will be devoted to Pennsylvania, which votes April 22 and offers 158 pledged delegates, the biggest prize left on the Democrats' dwindling campaign calendar.

As of Tuesday night, more than three-quarters of the states had voted, allocating more than 80 percent of the delegates to the Democrats' national nominating convention in August.

Given the math, it seems nearly certain that the party's superdelegates — Democratic leaders who get automatic entry to the convention — will settle the nominating fight.

In Mississippi, Obama won at least 17 delegates and Clinton won at least 11, with five delegates still to be awarded. In the overall race for the nomination, Obama had 1,596 delegates, including superdelegates. Clinton had 1,484, according to The Associated Press count.

It takes 2,025 delegates to secure the Democratic nomination at the party's national convention this summer.

Similar to voters in earlier contests, Mississippi voters said the economy was their greatest concern, with 9 in 10 polled saying the country's economic situation was bad.

Exit polls found that about half of such voters said that "change" was the most important quality in a candidate, topping the answers of "experience," "cares" and "can win."

Also, 55 percent of Tuesday's Democratic voters polled said that if Obama becomes the Democratic nominee, he should pick Clinton as his vice-presidential running mate. About the same number — 57 percent — said Clinton should add Obama to her ticket if she wins the nomination.