The Hollywood pair were spotted on two separate dates over the weekend, according to Life & Style magazine.
"Olivia was Bradley's date. He was always taking her hand or putting his hand on her lower back, it was really sweet. He took care of her all night," a source at the after-party for the premiere of Cooper's latest movie The Hangover Part II said.
"They were definitely together... [and] they left together. They seemed really comfortable with each other."
Cooper and Wilde have been romantically linked with other celebrities recently. Cooper, who split from Renée Zellweger in March after two years together, was rumoured to be dating Jennifer Aniston in April.
Wilde has been linked with Justin Timberlake after being spotted together on several occasions.
> Bradley Cooper: 'Hangover monkey was incredible'
Watch the trailer for The Hangover Part II below: