By early October, CBS Sports preseason No. 3 Oklahoma could either be the biggest frontrunner to reach the College Football Playoff again or completely out of the playoff picture. That's how difficult the Sooners' first six weeks are in 2016.

They open at a "neutral site" vs. No. 15 Houston in Houston. They're home against No. 6 Ohio State in Week 3 after a cupcake game with Louisiana-Monroe. They're at No. 13 TCU following a Week 4 bye. And finally, they play the annual Red River Rivalry in Dallas against Texas, which beat Oklahoma in two of the past three years.

It's arguably the most difficult opening schedule for a national championship contender in the past 25 years. In a way, it's the reverse of the Sooners' finish to 2015, when they knocked off No. 4 Baylor, No. 11 TCU and No. 9 Oklahoma State in three consecutive weeks to win the Big 12 before losing to No. 1 Clemson in the semifinals.

"We've always just believed if you're going to be a top-tier program and one of the better team in the country, play 'like teams,' challenge yourself," Oklahoma coach Bob Stoops said at Big 12 Media Days. "It's what college football fans all around the country want to see. I know it's what our fans want to see, as long as you win. But in the end, our players are challenged and excited about it as well as us as a coaching staff."

Three of Oklahoma's first four games come against top-15 teams in the preseason AP Top 25. If those rankings hold once the Sooners play each opponent, you'd have to go back to 1991 for the last time a preseason top-four team played three top-15 teams in its first four games. (We picked preseason top four because the CFP selects four teams.)

In 1991, preseason No. 2 Michigan beat No. 7 Notre Dame in Week 2 at home, had a bye, lost to No. 1 Florida State at home, and beat No. 9 Iowa on the road. The Wolverines finished 10-2, won the Big Ten and lost to national champion Washington at the Rose Bowl.

Since 1991, only three other preseason top-four teams opened their season with three of four games against top-25 opponents at the time:

  • LSU in 2011 vs. No. 3 Oregon, No. 25 Mississippi State and No. 16 West Virginia: LSU won all three games, won the SEC with a perfect regular season, and lost to Alabama in a BCS Championship Game rematch.
  • Ohio State in 1998 vs. No. 11 West Virginia, No. 21 Missouri and No. 7 Penn State: The Buckeyes won all three and finished 11-1 as the Big Ten champion with a final No. 2 ranking.
  • Washington in 1997 vs. No. 19 BYU, No. 7 Nebraska and No. 25 Arizona State: The Huskies lost the middle game to Nebraska and finished 8-4 with a final No. 18 ranking.
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Bob Stoops has quite the task in front of him. USATSI

Oklahoma players went through more intense workouts this summer, knowing they have to be ready from the start. The good news for the Sooners is they still have a loaded offense.

It's led by quarterback Baker Mayfield and probably the best one-two running back combo in the country, Samaje Perine and Joe Mixon. How good is Perine? According to Fox Sports, Barry Switzer compared the 5-foot-10, 235-pound Perine to Earl Campbell. Mixon averaged 6.7 yards per carry in 2015, tied for 24th in the Football Bowl Subdivision, and added 28 catches.

Oklahoma's offensive line is pretty young so that's a concern, especially in Week 1 against Houston's talented defensive line. But the Sooners' line was young last year, and they still won the Big 12. Perine and Mixon are adept at finding different ways to hurt defenses.

"These guys are such all-around players," Stoops said. "They're amazing when you watch the coaches' version of the end zone copy, the holes they pick and the patience they have. Then you notice the obvious is the strength and power and they rarely get caught. They're unusually fast guys for that size. So they have it all."

Gone is star wide receiver Sterling Shepard. The Sooners will look for Mark Andrews, Mykel Jones and Geno Lewis to stretch the field. Lewis is a graduate transfer from Penn State, where he had 55 catches for 751 yards in 2014 before losing playing time last season.

On defense, the Sooners return six starters but lost most of their marquee defenders. Four first-team All-Big 12 players are gone from a unit that led the conference in scoring defense last season.

They still have a solid defensive line led by Charles Walker. Cornerback Jordan Thomas and safety Ahmad Thomas returning in the secondary. It's just Oklahoma won't have the luxury of easing in some key new starters in 2016.

The best thing going for Oklahoma is Mayfield. He's a rare quarterback whose play inspires both sides of the ball. The Sooners will need his play-making ability and fearlessness to survive the first six weeks.