Over Oscar weekend in late February, art dealer Larry Gagosian held a private lunch at the $15.5 million home he recently bought in the Holmby Hills section of Los Angeles. His glass-enclosed house had been decorated for the occasion by the artist Richard Prince, so its walls were lined with his portraits of beach beauties and pulp-novel nurses.

As guests including financier Ron Perelman and actress Renée Zellweger navigated the home's skylit hallways, Mr. Gagosian and his staff mingled with guests, discreetly passing a rolled-up sheet of paper between them like a baton. The sheet listed prices for nearly every artwork in sight.

With an unrelenting focus on selling, Mr. Gagosian, 65, has become the most powerful art dealer in the world. He represents the estates and careers of 77 of the world's top artists, including Pablo Picasso, Alberto Giacometti, Cy Twombly, Richard Serra, Jeff Koons, Damien Hirst and Ed Ruscha. Dealers who track how he prices his gallery shows estimate he sells upwards of $1 billion worth of art a year. Sotheby's, by comparison, auctioned off $870 million worth of contemporary art last year.

As the contemporary art market rebounds from the recession, Mr. Gagosian's art empire is exploding. In the last few years, he has opened new galleries in London, Paris, Rome, Geneva, Athens and Hong Kong, expanding his global art network to 11 galleries world-wide—the largest blue-chip franchise ever attempted in the industry.