We all know that if Rick Santorum and Newt Gingrich want to be the Republican presidential nominee, they have to win more states. But they also have to win by large margins, The New York Times' Nate Silver explains, because so many states award delegates proportionally. So while a little gain in Alabama is good news for them, it isn't great. Here's our guide to today's polls and which ones matter.

Findings: There's essentially a three-way tie in Alabama, with Gingrich with 30 percent of the vote, Santorum with 29 percent, and Romney with 28 percent.
Pollster: Rasmussen
Methodology: Robo-calls to 750 likely Republican voters on March 8.
Why it matters: This poll sharply contradicts one released Thursday by the Alabama Education Association that showed Romney ahead by 10 points in the state, followed by Santorum with 21.6 percent and Gingrich with 21.2 percent. Which should be good news for either of these guys' chances for overtaking Romney, right? Yes. But. It helps to look at Alabama when thinking about how Santorum could come back from Romney's big lead in delegates, given that most of the remaining states award delegates proportionally. As The New York Times' Nate Silver explains, a small win for Santorum in those cases doesn't hurt Romney enough. In Alabama, if the final tally on March 13 is 35 percent for Santorum, followed by Gingrich and Romney tied with about 30 percent, then Santorum gets 21 delegates, while the others get 13 each. But if Santorum wins with 45 percent of the vote to Gingrich's 28 percent and Romney's 19 percent, then Santorum wins 33 delegates to Romney's 1 -- much better. But Silver writes that something pretty huge would have to happen in the race to give Santorum that kind of momentum everywhere. Gingrich, who's only won two states, has even further to go than Santorum.
Caveat: Rasmussen leans right, and there haven't been many polls in Alabama. 

Findings: Gingrich leads in Mississippi with 35 percent, followed by Romney with 30 percent and Santorum with 20 percent. Mississippi votes March 13.
Pollster: American Research Group
Methodology: Survey of 600 likely Republican voters on March 7 and March 8.
Why it matters: Gingrich's campaign has made it pretty clear he can't go on if he doesn't win the South. His huge lead is party thanks to his popularity among Tea Party supporters, 49 percent of whom say they're voting for him. Santorum is in third place among them with 17 percent, being beaten by Romney, who has 24 percent of Tea Partiers' vote.
Caveat: As explained above, for Santorum or Gingrich to win enough delegates to be the nominee, they have to not just win a lot of states, but crush Romney.

Findings: 65 percent of adults think the president and Congress can do something to stop gas prices from rising. And 85 percent of Americans think Washington should take immediate action to control gas prices.
Pollster: Gallup
Methodology: Interviews for the tracking poll with about 500 adults on March 5 and March 6.
Why it matters: They are, for the most part, wrong. But it explains why Gingrich -- and Michele Bachmann before him -- is campaigning on a promise to lower gas prices, arguing that gas prices might reach $9 under Obama and that Romney is too rich to understand high gas prices. 
Caveat: This week the national gas price average was $3.79 a gallon. Gallup finds $5.30 a gallon is the point where Americans think they'd have to seriously change their spending habits.