Top contenders for the 2015 Nobel Peace Prize

German Chancellor Angela Merkel, Pope Francis and a champion of rape victims are among oddsmakers' favorites to win this year's Nobel Peace Prize, which will be announced in Oslo at 5 a.m. ET on Friday.

Last year, the prize was awarded jointly to India's Kailash Satyarthi and Pakistan's Malala Yousafzai "for their struggle against the suppression of children and young people and for the right of all children to education."

Nobel winner Malala urges kids to stand up for rights

Each year, there is no shortage of worthy candidates for the six-member Norwegian Nobel Committee to consider. An estimated 270 people have been nominated but the Nobel Institute is always secretive about the selection process.

Here are candidates that oddsmakers rate as favorites to win:

ANGELA MERKEL

Germany's chancellor has demonstrated moral leadership this year on a topic that few other government heads have tackled head on: Opening her country's borders to up to 1 million refugees from conflict zones in Syria, Iraq, Eritrea and elsewhere. Not everyone in Germany supports Merkel's open-door policy and it remains to be seen how the country will absorb the huge influx of migrants.

MUSSIE ZERAI

Zerai, 40, an Eritrean Catholic priest, is the founder of an organization that has helped rescue migrants whose boats have encountered problems while trying to cross the Mediterranean Sea to reach Europe. He often takes calls in the middle of the night and relays GPS coordinates to the Italian coast guard.

POPE FRANCIS

The pontiff has had a good year. He played a key role in helping to normalize U.S.-Cuba relations after more than a half century, encouraged a long-sought peace agreement between the Colombian government and a rebel group, and weighed in with calls for sensitivity and common action to deal with issues such as climate change, economic inequality, immigrants and homosexuality. Francis was among last year's favorites to win the prize. No pope has ever won.

DENIS MUKWEGE

The gynecologist from the Democratic Republic of Congo and colleagues have treated more than 30,000 rape victims, risking his life in the process. In 2012, a gunman tried to murder him in his home. His name has been mentioned in association with the prize for several years.

JOHN KERRY/MOHAMMAD JAVAD ZARIF

Secretary of State John Kerry and his Iranian counterpart, Mohammad Zarif, are not favored by bookmakers, but there has been buzz for months that the historic nuclear deal they brokered in July should be recognized by the Nobel committee. Their intense diplomatic efforts over the past two years overcame many technical and political hurdles, as well as strong objections by Republicans in Congress and the Israeli government.

Below is a gallery of recent past winners of the Nobel Peace Prize.

And here are all of the Americans who have been awarded the Nobel Peace Prize.