Optimism is in the air around MLB, as all 30 teams report to Spring Training. Just a few months after the Kansas City Royals nearly became the most improbable World Series winners in years, other teams are looking at the defending American League champs as evidence that they can succeed in 2015.

Teams feel like they can build off last season’s successes and be improved after making additions in the offseason. Unfortunately, only one team will end the season as the champs.

It’s been 15 years since the defending champs repeated, and it will be difficult for the San Francisco Giants to win a fourth title in six seasons. Six other clubs, including four from the National League, have been given better World Series betting odds than the Giants. In the season following their last two championships, San Francisco failed to make the playoffs.

It won’t be easy for the Giants to make the postseason in 2015, considering the talent in their division. The top of the NL West is expected to be extremely competitive. The Los Angeles Dodgers won 94 games in 2014, and even though the San Diego Padres haven’t made the playoffs since 2006, the Padres made several upgrades this offseason. San Diego added the likes of Justin Upton, Matt Kemp and James Shields to their roster.

Even after reaching the World Series in October, the Royals are not considered to be a major threat in the AL. More than half of the Majors either has the same or better World Series odds than the Royals.

The Washington Nationals are the World Series favorites, entering Spring Training with 7/1 odds of winning it all. The Nationals led the NL with 96 wins last year, only to lose in the NLDS in four games. In 2012, Washington had the best record in all of MLB, and failed to make it to the NLCS. The Nationals made the biggest splash of the offseason, signing former Detroit Tigers' star Max Scherzer to a $210 million contract.

Even though the Boston Red Sox finished in last place last year, they’ve been pegged as the favorites in the AL. Boston signed Hanley Ramirez and Pablo Sandoval in the offseason.

After missing the playoffs for a second straight year, the New York Yankees aren’t predicted to be among the league’s best teams. With Derek Jeter gone, the entirety of the “Core Four” is retired, and the Yankees may no longer be the best team in the Big Apple. With a slew of young pitching and Matt Harvey ready to start the season as the team’s ace, the Mets (28/1) have better championship odds than the Yankees (33/1).

Below are the complete 2015 World Series betting odds for all 30 MLB teams, courtesy of Bovada.lv.

Washington Nationals 7/1

Los Angeles Dodgers 17/2

Chicago Cubs 10/1

Boston Red Sox 12/1

Los Angeles Angels 12/1

St. Louis Cardinals 12/1

San Diego Padres 14/1

San Francisco Giants 14/1

Chicago White Sox 16/1

Seattle Mariners 16/1

Detroit Tigers 18/1

Cleveland Indians 25/1

Oakland Athletics 25/1

Toronto Blue Jays 25/1

Baltimore Orioles 28/1

Kansas City Royals 28/1

New York Mets 28/1

Pittsburgh Pirates 28/1

Miami Marlins 33/1

New York Yankees 33/1

Houston Astros 50/1

Texas Rangers 50/1

Atlanta Braves 66/1

Cincinnati Reds 66/1

Milwaukee Brewers 66/1

Tampa Bay Rays 66/1

Arizona Diamondbacks 100/1

Minnesota Twins 100/1

Colorado Rockies 150/1

Philadelphia Phillies 150/1