IT COULD HAVE been worse - a lot worse.

None of the seven CSX cars - six of them loaded with volatile crude oil - that derailed on the 128-year-old rail bridge over the Schuylkill between University City and Grays Ferry about 12:30 a.m. yesterday fell onto the busy expressway, which would have risked a fiery conflagration.

And none of the oil-laden tanker cars - criticized by experts and environmentalists as too easy to rupture - broke open and spilled into the waterway as they tilted precariously, although the Coast Guard rushed a boat to the scene and placed booms across the river just in case.

The first city derailment since the former Sunoco refinery reopened last year under new ownership - largely handling rail shipments from the booming Bakken oil field in North Dakota - wasn't a catastrophe like what happened last summer in Quebec, where a runaway train exploded in the dead of night, killing 47 people.

But that did little to mollify critics who are ever more alarmed that Philadelphia's 21st-century oil rush is happening with far too little regulatory oversight and too many questions about the region's crumbling infrastructure.

"We're playing Russian roulette here," said David Masur, director of Philadelphia-based PennEnvironment. He and other experts worry that major derailments and explosions over the last six months in Quebec, Alabama and, most recently, North Dakota are revealing a dark side to North America's recent surge in oil production.

Jacksonville, Fla.-based CSX said in a statement last night that it still didn't know what caused the derailment of the train traveling from Chicago to Philadelphia with two locomotives and 101 freight cars. It said the seven cars at the rear derailed, but that no one was injured and no oil or sand - the cargo of the seventh car - was released.

The rail line also had no immediate information on when freight traffic across the Schuylkill Arsenal Bridge would resume. The CSX statement said work was beginning last night to carefully recover the oil and sand from the derailed cars, an operation that could take as long as 48 hours. A full tanker car can contain nearly 700 barrels of crude.

The oil was headed to Philadelphia Energy Solutions, the historic South Philadelphia refinery reopened last year by a joint venture of prior owner Sunoco and the Carlyle Group, christening a new $100 million rail terminal and creating more than 1,000 jobs. The firm issued a statement last night that "Philadelphia Energy Solutions will continue to monitor the situation and provide whatever assistance we can."

Just last month, the Daily News reported that the South Philly refinery was already planning to double rail traffic early this year - to a total of 5 million barrels a month - even as the sharp rise in accidents was raising safety questions. Experts fret about the propensity of North Dakota crude to catch fire in an accident - either because of the oil's makeup or because of other volatile chemicals used in fracking - and that America's aging fleet of tanker cars has too many safety and design flaws to properly transport the oil.

That's not the only issue around aging. The landmark wrought-iron Arsenal bridge, on which the derailment took place, was completed in 1886 during Grover Cleveland's first term as president. From the bridge, CSX trains rumble through South Philadelphia on a milelong 25th Street overpass where, the Daily News reported in a separate article last summer, residents have been complaining to CSX and city officials about crumbling concrete and disrepair.

John Hanger, a former Pennsylvania environmental-protection commissioner running as a Democrat for governor, said he would call today for a series of moves to strengthen oil-by-rail safety - including a statewide safety conference that would look at issues like the volatility of the oil, a mandate to phase in newer and stronger tanker cars, and a levy on rail shipments into Pennsylvania to pay for training of first responders.

"The potential for a mass-casualty disaster is real," he said.