But the police stumbled upon the racket after reports of an explosion in the residential locality at around 9 pm on Tuesday. No one was reported injured.
The tunnel was about 2.5 feet wide, enough for a man to crawl to the other end of the tunnel.
Zubair, a scrap dealer, is accused of have started digging the tunnel from a compound in the area that also served as a godown.
He has been arrested and a hunt for his accomplices launched. The police said they were trying to ascertain the nature of support the gang of thieves received to dig the tunnel.
Neighbours told NDTV that they had never noticed him taking out large amount of soil from the house.
In his initial interrogation, a police officer said Zubair is reported to have told the police that it had taken them three months to dig the tunnel and they had drilled into the pipeline just a few days ago.
"It seems that they had starting siphoning the fuel for just three-four days," the officer said. They apparently were still on a learning curve, one reason why the explosion could have been triggered by their carelessness.
This, however, isn't the first time that fuel thieves have been caught tapping into oil pipelines in west Delhi.
In February last year, the police busted a gang of thieves that claimed to have drawn fuel worth crores from oil pipelines near the Mathura refinery. According to the police, the mastermind in this case had been puncturing pipelines for nearly a decade.
The last such case to have been reported in Delhi was in 2009 when a factory owner was arrested for digging a 1-km long tunnel to draw petrol from a pipeline, also in west Delhi Mundka.