Nearly at the halfway point of college football's regular season, there are 13 FBS schools still undefeated. That's about average -- the last couple seasons have seen anywhere from 10 to 16 teams undefeated at this point -- and so is the whittling down process from double-digit undefeateds to just a couple teams, maximum, by the end of the regular season. 

Since history tells us that the list will be thinning as the season progresses, we've ranked the baker's dozen of unbeaten based on their chances to finish the regular season without a loss.  

1. San Diego State Aztecs (6-0)

Toughest game remaining: vs. Boise State (Oct. 14, 10:30 p.m. ET, CBS Sports Network) 

Why they could win them all: The Aztecs have proven to be the class of the Mountain West this year. Rashaad Penny ran for more than 1,000 yards last year as a backup to Donnel Pumphrey, and now he's 25 yards shy of matching that total through six games (on pace to flirt with 2,000 yards) as the new featured back. The toughest games on the schedule are past with wins against Arizona State and Stanford, and if they beat Boise State this weekend, I think the odds are in their favor to finish the regular season undefeated.    

Why they could lose: If San Diego State falls to anyone other than Boise State or New Mexico (Nov. 24), it's going to be a stunning upset, and both of those remaining games are at home. You could point to common reasons for losses like attrition or the fact that any team could creep up and knock off a favorite in college football, but I think the Aztecs will head to the Mountain West title game 12-0.   

2. Alabama Crimson Tide (6-0)

Toughest game remaining: at Auburn (Nov. 25)

Why they could win them all: Other than Auburn, there is no one on the regular-season schedule who I'd give more than a 10 percent chance of beating Alabama. Mississippi State gets the Tide in Starkville, Mississippi, this year, but even if Nick Fitzgerald gets hot, it's hard to imagine the Bulldogs' defense getting enough stops against Alabama rushing attack. 

Why they could lose: Auburn is heating up, and by the time it plays  Alabama in the Iron Bowl, the Jarrett Stidham-Kerryon Johnson offense might be executing at SEC Championship levels. Arkansas, Tennessee and LSU are going to be games where Alabama might yawn a little bit, but the potential loss is in Jordan-Hare Stadium on Thanksgiving weekend. 

3. Clemson Tigers (6-0)

Toughest game remaining: at NC State (Nov. 4)

Why they could win them all: Because Florida State is down this year and the Georgia Tech game is at home. The program depth on display this year at Clemson is not just a compliment to talent acquisition but also talent development. Blue-chip prospects like Christian Wilkins, Dexter Lawrence and Travis Etienne play right away, but the team is anchored by veterans like Dorian O'Daniel, who spent a couple years in the program and have emerged as stars later in the career. That balance of raw talent and leadership is something every coach strives to achieve because it keeps Clemson in check during the grueling path to a title. 

Why they could lose: The path to a 28-2 record across 2015 and 2016 included a lot of close, nail-biting wins and a shootout loss to Pittsburgh at home. Clemson is the closest thing we have to seeing a team "clutch gene" in college football, but if outcomes start flipping in these close games, there's a loss hiding later in the schedule. NC State had a 33-yard field goal attempt to beat Clemson last year and missed it before losing in overtime, and it's gotten even better since that 2016 meeting. Florida State and Georgia Tech are tough outs, but beating the Wolfpack might be the last big hurdle for the Tigers going 12-0. 

4. UCF Knights (4-0)

Toughest game remaining: at Navy (Oct. 21) 

Why they could win them all: There has been more attention given to Charlie Strong and South Florida, but after four games, I feel confident naming the Knights, not the Bulls, as the favorites to win the American Athletic Conference. The division will be decided when UCF and USF play in the regular-season finale on Nov. 24, and if both teams are still undefeated I give the Knights the edge.   

Why they could lose: The Navy game could end up being a shootout. It's way too volatile of a contest to feel confident on either side, but even if the Knights lose on the road in Week 8, they'll still have a chance to clinch the division against USF and potentially get a rematch in the AAC title game. 

5. South Florida Bulls (5-0)

Toughest game remaining: at UCF (Nov. 24)

Why they could win them all: Outside of the rivalry game against UCF, the Bulls are going to be favorites -- likely by at least a touchdown -- in every game left on their schedule. The offensive firepower with Quinton Flowers under center is too much for many teams to match, and as long as they avoid an upset loss (Tulane on the road on Oct. 21 looks tricky), the regular-season finale will be the toughest and final test. 

Why they could lose: It's worth considering that, during this 5-0 start against lesser competition, USF hasn't gotten a chance to play its best football in a tight game. What happens when this run of 20-30 point wins comes to a halt and USF finds itself in a close game? 

6. Washington Huskies (6-0)

Toughest game remaining: at Stanford (Nov. 10)

Why they could win them all: It took a few weeks, but Washington has warmed up and is rolling right now. The ground game is moving with rhythm, and the defense has developed an edge of domination, making the Huskies look like the most dangerous team in the Pac-12. Criticize the schedule all you want, but it's allowed Washington to work itself into peak condition as Pac-12 play begins. Staring down a remaining schedule that has no USC, it's easy to feel good about Washington's chances.  

Why they could lose: While the team's play is consistent enough to like its chances of going undefeated, the schedule still has a pair of traps (at Arizona State on Saturday, at Stanford in November on a Friday night). But the game that's going to generate the most hype and attention is the Apple Cup against Washington State. I don't expect more than one loss, but a loss in any of those three games would not be a huge surprise. 

7. Wisconsin Badgers (5-0)

Toughest game remaining: vs. Michigan (Nov. 18)

Why they could win them all: No one else in the Big Ten West is playing on Wisconsin's level. The toughest game and only potential loss in the regular season is when Michigan comes to town and even getting that game at home is favorable. 

Why they could lose: While Wisconsin is playing better than everyone else in the division, it is not free from injuries, bad luck or close calls. Things could go sideways against Michigan, at Minnesota (Nov. 25) or at Indiana (Nov. 4), but luckily for the Badgers, it likely wouldn't derail their path to the Big Ten Championship Game. 

8. Georgia Bulldogs (6-0)

Toughest game remaining: at Auburn (Nov. 11)

Why they could win them all: Defense travels well in the SEC, and the edge defenders on Georgia's front have been playing some of the best football you'll see anywhere at any level. That is going to be a key against Auburn's multi-faceted attack, and the chess match between the two sides is going to make it one of the best SEC games of the year. Georgia should win every SEC East game, making the Auburn game the final domino to fall for an 8-0 conference record. 

Why they could lose: Because that Georgia Tech game on Nov. 25 is dangerous enough on annual basis, could you imagine the tension if Georgia is undefeated? The SEC East could be locked up and while coaches, players and fans are starting to think about Alabama in Atlanta there's a quick stop off to Bobby Dodd Stadium to face Paul Johnson. I think Georgia will win the SEC East with a 7-1 or 8-0 conference record, but if I were a Dawgs fan, I'd be terrified at the playoff implications on the line against the Yellow Jackets. 

9. Penn State Nittany Lions (6-0)

Toughest game left: at Ohio State (Oct. 28)

Why they could win them all: Penn State has the best college football player in the country on its side in Saquon Barkley. There have been crucial moments of games where his individual playmaking ability has totally changed the game, and with a schedule that has three great defenses left to play, it's nice to have the best offensive weapon around on your side. 

Why they could lose: The Nittany Lions escaped Iowa with a walk-off win, battled through a slow start against Northwestern and yet the schedule still has the toughest games with Ohio State, Michigan State and Michigan. As of right now, I favor Ohio State in Columbus and wouldn't be shocked if Michigan State is an even tougher road trip than Iowa. 

10. Miami Hurricanes (4-0)

Toughest game remaining: vs. Notre Dame (Nov. 11)

Why they could win them all: Virginia Tech and Georgia Tech both have to come to Miami while North Carolina and Pittsburgh have both taken a step back in 2017. Even the toughest games left in ACC play look manageable after edging Florida State in Tallahassee last week. If Miami can knock off Notre Dame at home, it sets up for a potential playoff run. 

Why they could lose: Injuries have already become a season-defining issue for Miami with the loss of star running back Mark Walton. While the odds favor a double-digit win season, I think the chances of navigating the entire ACC schedule and Notre Dame without one loss is unlikely. 

11. TCU Horned Frogs (5-0)

Toughest game remaining: at Oklahoma (Nov. 11)

Why they could win them all: The most impressive thing about TCU's profile is that they've been able to win in lots of different ways. The Arkansas game was a grind, SMU was a shootout. Against Oklahoma State, it got the lead early and defended it when Mason Rudolph mounted a charge and against West Virginia they went blow-for-blow and came up big with clutch plays. The location or style doesn't seem to matter, because Gary Patterson's group is playing winning football. 

Why they could lose: As we've seen over the last couple of weeks, the Big 12 schedule is packed with potential losses. Beating Oklahoma in Norman worked out for Iowa State, but I doubt the Sooners let that happen twice. Texas Tech and Kansas State are both dangerous road trips and Texas is going to be tough out when they come to visit on Nov. 4. 

12. Washington State Cougars (6-0)

Toughest game remaining: at Washington (Nov. 25)

Why they could win them all: There are three really tough games left for Washington State, and they're all in November. The Cougars play Stanford, at Utah and at Washington in the final four weeks of the regular season, and if they get through the first two games undefeated I'd give them a 50-50 shot of knocking off the Huskies in the Apple Cup. 

Why they could lose: Beating USC and starting undefeated has put Washington State in the spotlight but the variance of performance suggests there's a loss somewhere ahead on the Pac-12 schedule. They can take a loss and still win the Pac-12 North with an Apple Cup victory, but I think undefeated is an unlikely outcome for the Cougars at the end of the regular season. 

13. Navy Midshipmen (5-0)

Toughest game remaining: at Notre Dame (Nov. 18)

Why they could win them all: Navy will contend for the AAC title, but I don't yet feel confident saying it could win all its remaining games. Zach Abey ranks second nationally in rushing and has a done great job leading the offense in close games, but the defense isn't strong enough right now to think they'll finish the regular season undefeated. 

Why they could lose: Notre Dame is really good, UCF is really good, and even this weekend's game against Houston is a spot where Navy could slip up. With a suspect defense and plenty of tough games, it makes at least one loss look likely. Navy will, however, be in the thick of the conference title race, and as long as it beats division opponents, should have a shot at New Year's Six consideration.