He and Con Edison officials say that even though the gas remains flowing, there is no danger of fire or explosion because oxygen would be necessary for a spark, and the gas mains are oxygen-free. The robot enters and exits the main through a “launch tube” from which oxygen is expelled before the robot slides into the main. The robot, controlled by a technician in a trailer on the street, goes into the gas main at the start of the workday and comes out at quitting time.

The robot has proved so reliable that it has found work in other parts of the United States and in other countries. It goes by the matter-of-fact name Cisbot (pronounced SISS-bot), for cast-iron sealing robot. As the acronym suggests, the gas mains the robot travels through are made of cast iron.

Mr. Kodadek did some calculations. On the stretch of West End Avenue between West 102nd and West 103rd Streets where the robot was working on a recent sunny morning, he said, there were about 109 joints in the gas main beneath the pavement.

So, he said, 109 holes did not have to be drilled.

The robot is also less expensive than the old methods of maintaining the mains. John Ciallella, Con Edison’s section manager for gas engineering reliability, said that hiring ULC Robotics for the work with the robot on West End Avenue cost $400,000. To do the job the way such work used to be done would have cost $1.5 million to $1.8 million, he said.

Baby boomers old enough to remember Erector sets might think Cisbot was constructed from the parts bins of their childhoods. It is long, heavy on the metal, not terribly stylish and somewhat short on personality — unlike, say, BB-8 from “Star Wars.”