It's 30 minutes before game time at Camden Yards, and Greg Schwalenberg peers out at the vast expanse of empty green seats. He grimaces.

"What kind of crowd are they expecting?" he asks a nearby usher.

"Let's see, 10,000," the man replies.

"It's been this way most of the season," Schwalenberg says with a weary smile.

Schwalenberg has sold beer at Orioles games for 31 years, and he knows that with four empty seats for every one filled, he'll have to scramble all over the outfield stands to sell enough Budweisers and Bud Lights to turn a solid profit for the evening. But when he emerges after the first pitch with his blue plastic tub full of bottles and ice, his face bears no sign of frustration.

"Cold beer here! Budweiser, Bud Light. Beer man!" he calls as he bounds halfway down one aisle, then cuts across an empty row. Every so often, the 58-year-old pauses, holds up a bottle of each beer and casts an inviting grin at the fans before him. But he rarely stops prowling for the next section where he might find a thirsty soul.

Vendors work on commission, earning 16 percent of their gross sales plus tips. It's a hustle game.

If you've ever passed a balmy afternoon in the bleachers at Camden Yards and craved a crisp Budweiser, chances are you bought that beer from Schwalenberg. If you haven't enjoyed his work in the stands, maybe you've toured the Sports Legends Museum in the adjacent warehouse and gazed at one of the exhibits Schwalenberg lovingly prepared as curator.

Though he has never thrown a strike or signed a home-run hitter, the Pigtown resident's prints are all over the experience of enjoying baseball in this town.

Schwalenberg has ranked among the five highest-earning vendors since the park opened, right up there with fellow veterans "Fancy" Clancy Haskett and Howard Hart.

This isn't a point of pride so much as a key to continuing prosperity. The vendor rankings come out three times a year and determine the order of the nightly product draft in the bowels of the warehouse. About 10 minutes before game time, the vendors gather in a room of brick walls and exposed pipes. One by one, they say which product they'll sell and which supply room they'll draw from, and thus, which section of the park they'll work.

Because he's always near the top of the rankings, Schwalenberg knows he'll get his trusty Budweiser and Bud Light from his favored supply room, located just outside the left field bleachers.

"It's a lot easier to stay on top than to get there," he says.

Earnings for vendors have dropped along with attendance at Camden Yards, but top beer salesmen can still make $200 to $300 on a good night. The work has afforded Schwalenberg luxuries he couldn't have enjoyed otherwise, not all of them financial.

Vending has given him some of his best friends, paid for a trip to Italy and put him in the stands when Cal Ripken trotted out for his 2,131st consecutive game and when Muhammad Ali lit the Olympic torch (he was working in Atlanta for Aramark).

Schwalenberg grew up in Baltimore, and his life was rich with baseball and museums from early on. His grandfather worked the graveyard shift at Sparrows Point, so he had afternoons free to take the boy to ball games (Schwalenberg's favorite Oriole was Ron Hansen.) On the way home, they often stopped at the Baltimore Museum of Art.

Schwalenberg was working at the Walters Art Gallery (now the Walters Art Museum) in 1979, when he saw an ad in the newspaper seeking vendors for Memorial Stadium. He often took the bus up to games anyway, so he figured why not supplement his modest income?

He picked a heck of a season to start. It was the birth year of Orioles Magic, conjured in part by Wild Bill Hagy, a bearded baseball shaman who drove a cab by day and led cheers from the upper deck by night.

Schwalenberg quickly showed a salesman's instinct by zeroing on Hagy and his tribe of rowdies in Section 34. Sure, the superfans showed up with their packs of Budweiser and Busch but they rarely took long to run through those.