Since Santorum is the only other candidate who can be nominated, so far, he needs to win three states, or he should withdraw and plead with his supporters to support Santorum. At the moment, that is the only alternative to a Romney nomination.
Best bets:
Louisiana - currently 3rd
Wisconsin - distant 3rd
North Carolina - 3rd
Texas - 3rd
(recent polls)
He was leading in WV, NE, and MT, but that was back in November.
Arkansas, Kentucky, and South Dakota have no polls I can find.
You don’t seem to understand what many of us here have understood for awhile. This race is now about denying Romney delegates and forcing a brokered convention. Santorum can not win the nomination outright. Romney’s best chance to win outright is if Newt drops out because half of Newt’s support would go to Romney.