The 2016 audience for the ABC Television broadcast was the second-lowest on record for an Oscars ceremony. The least-watched Academy Awards show since Nielsen began tracking Oscars in 1974 came in 2008 when about 32 million Americans tuned in.
The low figures came despite the presence of Leonardo DiCaprio, who won his first Oscar, and anticipation about how host Chris Rock, who is black, would address the furor over an all-white line-up of acting nominees.
It was not immediately clear on Monday whether the smaller TV audience reflected calls by civil rights leader Al Sharpton for a "tune out" to protest the absence of people of color among the nominees.
The restricted appeal of some movies, including best picture winner "Spotlight" about sexual abuse in the Catholic Church, and "Room," which brought rising star Brie Larson an Oscar, also may have been a factor, awards watchers said.
About 40 people turned up to a protest rally, organized by Sharpton, in Hollywood on Sunday night.
"Though clearly we don’t take full credit for the decline (in the TV audience), certainly one would have to assume we were effective and part of the decline," Sharpton said in a statement on Monday. "And to those that mocked the idea of a tune out, it seems the joke was on them."
Rock, hosting the ceremony for a second time, got generally warm reviews from fellow celebrities and media critics.
"That was really incredible," tweeted former Oscars host Ellen DeGeneres.
Comedian Amy Schumer said, "Welp @chrisrock murdered #oscars," and talk show host Oprah Winfrey gave Rock two thumbs up, adding "@chrisrock now you Breathe!"
Variety's Brian Lowry said Rock "brilliantly threaded the needle with his opening monologue." But Lowry said Rock and the show's producers "went back to that issue a few times too many (and less sharply)" later in the evening.
DiCaprio's expected best actor win drew more than 440,000 tweets per minute, making it the most-tweeted minute of an Oscars telecast ever, according to Twitter. The Oscars generated 24.2 million tweets globally throughout the night, Twitter said.
On Facebook, 24 million people engaged in 67 million interactions related to the Oscars, with DiCaprio's win once again notching the most talked-about moment, according to Facebook figures.