The 2018 show had reached only 26.5 million viewers, a figure that set off alarm bells at ABC and the motion picture academy.
This year's show featured movies with more box office juice than in the recent past. It provided a water-cooler controversy over the merits of best picture winner "Green Book," and some memorable musical performances by Queen and the duo of Lady Gaga and Bradley Cooper.
It also went without a host after Kevin Hart backed off, although the trio of Tina Fey, Amy Poehler and Maya Rudolph offered what was essentially an opening monologue.
The Oscars is generally the most-watched entertainment program of the year, often only second to the Super Bowl. Yet its viewership had declined steadily since hitting 43.7 million in 2014, the Nielsen company said.
Despite this year's rebound, it still represents only the second time since Nielsen has been measuring that viewership slipped under 30 million people.
The biggest Oscars audience ever recorded came in 1998, when 55.2 million people turned out to see "Titanic" named best picture.
ABC also said Monday that its preview of the drama "Whiskey Cavalier" was seen by 4.2 million people after the Oscars ended.