A little more than a year ago, Instagram opened its photo feed to advertisers large and small. Now, more ads are coming to the free app — this time through Instagram Stories, a successful feature it introduced in August.

The company, owned by Facebook, said 150 million accounts a day were now using Instagram Stories, which made waves for its mimicry of Snapchat Stories. That is half of Instagram’s 300 million users a day.

While people might post carefully filtered photographs of their new dogs to Instagram’s regular mobile feed, the Stories feature enables them to showcase a more spontaneous collection of images and short videos, which disappear after 24 hours — say, a clip of tug of war and images of a dog’s snout and eyes with silly captions and emojis.

Ads will now show up between some Stories, which take up the full phone screen and otherwise seamlessly transition from one account to the next. (Snapchat, which has 150 million daily users over all, runs similar ads.) Instagram will soon begin with ads from more than 30 companies — including General Motors, Netflix, Airbnb and Capital One — before expanding to all advertisers in coming weeks. It will monitor feedback to determine how often the ads will appear, said James Quarles, the vice president of Instagram Business.