In a city of glittering office towers and computerized transactions, of records kept in the cloud and fuels that send less soot into the sky, the authorities say old-fashioned corruption of the most brazen kind still poisons the heating oil industry.

Drivers carry guns to guard their cash. Hidden paper records document fraudulent dealings, and then disappear by the end of the season. Deliverymen pump air into the fuel tanks of homes and municipal buildings, and use magnets to throw off the meters that are supposed to make sure oil is flowing through the hose, the authorities say.

The rituals of the trade are so routine as to pass the notice of most New Yorkers, with drivers working at odd hours and in freezing temperatures, venturing into crawl spaces forgotten even by building superintendents.

But on Tuesday, the authorities pulled back the curtain on industrywide fraud that they said had festered for decades, despite promises by city officials over the years to clean up the trade. The Manhattan district attorney’s office unsealed indictments against 44 people and nine companies, which officials said revealed institutional corruption that had affected buildings including homeless shelters, hospitals, courthouses, police precinct station houses and prison buildings on Rikers Island. Many customers, officials said, were defrauded of as much as 10 percent of the oil that they believed was being delivered.