Lindsay Lohan Parties with Sean Penn

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Is Lindsay Lohan trading up?

A Celebuzz source spotted the 22-year-old starlet partying at West Hollywood's Nobu last night with actor Sean Penn.

"Sean was the only guy at a table full of Lindsay and her friends," the source tells us of the sushi hotspot festivities. "The whole table chatted and chain-smoked."

Lindsay was looking "super skinny" in a sheer white top and a pair of her signature black leggings, while the spy tells us 48-year-old Penn was wearing a hoodie and jeans looking like an "unmade bed."

This isn't the first social outing for the odd couple—in December of last year the two were spotted together at The John Dory, a downtown New York City spot where Penn hosted a private dinner for his awards-favorite flick Milk (where speculation said the actors discussed starring in a film together).

While no nuzzling went on at Nobu, as was noted in their NYC romp, our source says the two definitely looked "comfortable."

This is the second consecutive solo outing for Lohan, who is rumored to be single after a breakup with DJ Samantha Ronson at the top of the New Year.

On Tuesday, Celebuzz spies caught Lohan partying at LA's Apple Lounge with girlfriends. According to the actress herself, however, she and Sam are just fine.

A paparazzi camp stationed outside of Ronson's home in the Hollywood Hills caught Lohan exiting yesterday. When asked if the two split, Lohan gave an exasperated "No."

Check out the clip:

Penn will be seen next on NBC's Sunday telecast of the Golden Globes, where he'll compete for Best Actor in Drama for his turn in Gus Van Sant's Harvey Milk biopic.

Also spotted at Nobu: rapper Eve and actress Sanaa Lathan.