The actress, 40, kicked off Friday night at CAA's pre-Golden Globes party at the Buffalo Club in Santa Monica. There, she ran into rumored former flame Bradley Cooper, with whom she shared a brief hug.
Aniston spent much of the evening chatting with Gerard Butler, her costar in The Bounty Hunter, due out in March.
"Jen looked amazing in a short, black dress," says one observer. "She was also in a great mood, a social butterfly and mingled for almost three hours. … Gerard entertained Jen, and Jen kept giggling like she always does with Gerard."
Aniston – all smiles and as bubbly as ever – spent quality time with Butler on Sunday night, too, as they attended the Golden Globes at the Beverly Hilton, joining David Arquette and Courteney Cox for much of the evening.
At one point during the party, another ex-boyfriend, Tate Donovan, came over to say hello, and Aniston seemed thrilled to see him. "Tate! How are you!?" she cried.
Butler was last seen chatting up Avatar's Zoe Saldana in the valet line.