Exit polls indicated that Louisiana's primary saw a high turnout of voters who identified as very conservative — a group that has typically favored Santorum. Also helping Santorum was a high turnout of religious voters — nearly two-thirds of voters in today's primary said that they go to church at least once a week.
Santorum is Romney's chief challenger and a former Pennsylvania senator who has won previous contests in Tennessee, Mississippi and Alabama.
A Louisiana victory is unlikely to change the overall dynamics of the race. Santorum still dramatically lags Romney -- the former Massachusetts governor -- in the hunt for delegate to the GOP's summertime nominating convention. Former House Speaker Newt Gingrich of Georgia was far behind in the Louisiana vote count.
The Associated Press contributed to this report