A quarter-century ago, the animated comedy “The Simpsons” put the fledgling Fox network on the map as the fourth broadcast network. Now, with a much-promoted marathon of all 552 episodes that ended Monday, “The Simpsons” has repeated that feat, lifting a year-old cable channel called FXX to the top ranks of the 105 cable networks measured by the Nielsen Company.

The 12-day, round-the-clock marathon, which also included the two-hour 2007 theatrical movie, produced ratings about three times as high as executives at the channel expected. It enabled FXX to finish as the highest-rated network in all of cable television among the audience most desired by advertisers — viewers between the ages of 18 and 49 — three nights out of 12. For its full run, the audience for the marathon had a median age of 28, one of the youngest in the television business.

Beyond validating “The Simpsons” as a cultural phenomenon almost without parallel in television history, the marathon will create another significant result, said John Landgraf, the chief executive of FX networks. “We are talking about a radical transformation of asset value,” he said.

The channel FXX sprang from the Fox Soccer Channel, which “had an asset value of nil.” Mr. Landgraf said.