Justin Timberlake has fuelled rumours he's getting serious with new girlfriend Jessica Biel by shopping for rings.

Biel recently quashed reports she'd be walking down the aisle with the pop star anytime soon explaining, "What's weird is: You're single for 20 or 30 years, and you're married for like 70. It doesn't seem like a good ratio, does it?"

But her firm words haven't deterred Timberlake, who reportedly snapped up a promise ring in Santa Monica, California, recently to make their relationship more official.

A source tells Life + Style magazine, "Justin isn't ready to propose, but he wants to make a commitment to her.

"Justin says Jess is his dream girl. He wants to give her a symbol of his affection and love."

The couple has been dating since May.