As in Tennessee, ideological and religious commitment provided Rick Santorum with a win in the Oklahoma GOP primary, denying Mitt Romney a victory in any of the three fully contested Southern states.

Nearly half of Oklahoma voters called themselves very conservative, higher than in any other primary state this cycle, or in previous years within the state. And they broke heavily for Santorum - 45 percent to Newt Gingrich's 28 percent and Romney's 19.

Religion also was a big factor - nearly three-quarters of Oklahoma Republican voters were born-again Christians, among the most in any state this year, and seven in 10 said it's important to them that a candidate shares their religious beliefs. Santorum won these groups by 17 and 23 point margins, respectively.

Among those who said shared religious beliefs mattered "a great deal," moreover, Santorum won by a vast 36-point margin.

Nearly half in Oklahoma were looking chiefly for a candidate with "strong moral character" or for a "true conservative," more than in any other state, and more combined that the number focused on electability, Romney's forte. Among "moral character" and "true conservative" voters. Santorum won 58 percent support, compared with 18 percent for Paul, 12 percent for Gingrich and just 11 percent for Romney.

The Oklahoma electorate also was lower-income than most so far this year, another boost for Santorum's favor. More than four in 10 voters reported incomes less than $50,000 a year -10 points more than in 2008 - and they backed Santorum by a 15-point margin over his nearest competitor.

Santorum was more competitive than elsewhere in some of Romney's customarily stronger groups - college graduates, wealthy voters and self-identified Republicans. And Romney held tightly to his perceived electability: Among the nearly four in 10 voters who called electability the most important quality in a candidate, 43 percent backed Romney, 32 percent Gingrich, just 22 percent Santorum.