From its first hamburger and root beer stand in Shawnee, Okla., in 1953, the company built a stronghold in the Southwest, especially Texas, where there are just under 1,000 Sonic drive-ins.
The menu has the usual burgers, chicken, shakes, and malts. But also tater tots, ched "r" peppers - jalapeo peppers filled with cheese and deep fried - and an extra-long chili-and-cheese hot dog
Then, there are 168,000 drink combinations - or so Sonic claims - that diners can custom-order: cherry limeade with fresh limes, real fruit slushes, flavored ice tea, orange strawberry root beer float, cherry vanilla Dr Pepper.
"We started in Oklahoma, and then went south, north, east and west," said Drew Ritger, Sonic's senior vice president of business planning and purchasing, at the firm's headquarters in Oklahoma City.
Philadelphians may know Sonic best from its television ads.
The company spends $90 million to $100 million a year on national advertising, mostly satellite and cable television and the major networks, and an additional $90 million to $100 million on local advertising, such as billboards, radio, and newspapers.
"In Philadelphia, you are seeing national advertising that has been going on for at least five years," Ritger said.
Sonic opened its first drive-in here about two years ago, after settling first in the Harrisburg area, and Morgantown, Ephrata, and Reading about four years ago.
"The brand was just phenomenally accepted there, and a lot of people from Philadelphia asked about Sonic," Ritger said. "We felt like we would do well."
Today there are 24 Sonics in Pennsylvania, 11 in New Jersey, four in Delaware, and three in New York.
About 90 percent of the drive-ins across the country are individually owned and operated by franchisees.
Patrick Lim, 24, and his father, Jaime Lim, 54, a retired physician, live in Bucks County and run five Philadelphia-area Sonics.
"We are actually from Texas, so I grew up with Sonic," Patrick Lim said. "I went to school at New York University, so being up here in the Northeast for the past five or six years, I noticed that Sonic wasn't up here."
"People had been seeing the commercials, wondering what it is, so we both thought it would be a great opportunity to bring it up north."
In August 2008, the Lims opened their first Sonic in Bensalem, on Street Road. "The response has been great," said Jaime Lim. The Bensalem opening was the second-most successful in revenue in Sonic's history at that time, they said. They would not discuss individual restaurant revenue, citing corporate policy.
Sonic's strategy is to open two or three new restaurants a year in an area.
"We don't grow at a very fast clip," Ritger said. "The most important thing is having the right people running them. We don't go in a market and open 25 stores all at once."
"People ask all the time, 'Well, it's a drive-in concept; in the winter how do you do?' " While winter is not Sonic's busiest season, "it's pretty similar to any other restaurant brand," he said.
"January is always your lowest month. As long as the weather is just normal, people are out, and we do reasonably well. Obviously, when you get 60 inches of snow, I doubt any business in Philadelphia is doing fantastic in the last month."
At lunchtime yesterday, more than a dozen cars had pulled into stalls.
"I'm glad they came. I think we'll be here quite often," said Feasterville resident Bob Lewis, having lunch with his wife, Connie, and daughter, Amy.
"We first were introduced to Sonic out in Lancaster County," Connie Lewis said. "We couldn't find any around here until they opened in Bensalem. I really like it, especially their drinks, which are very unique."
"Oh, my, they are fantastic!" her husband said.
Cindy Zieminski, of the city's Somerton section, had her car window down, about to order. "We live around the corner, and my 17-year-old daughter goes to Sonic all the time. That's why we decided to come."
"I think it's pretty cool," daughter Brandi Zieminski, 15, said.
"It's creative," chimed in a friend, Jamie Gogel, 15, from the backseat, "because no one would ever think of a restaurant like this."
"My older daughter, Nicole, goes to the Sonic on Street Road with her friends once a week," said Cindy Zieminski. "Maybe 10 cars, all their friends go. They meet up, they park, and eat together. She always talks about it. I was like, 'Ah, well, we'll check this place out!' "
Contact staff writer Linda Loyd at 215-854-2831 or firstname.lastname@example.org.