Los Angeles - Phil Orlins knows everything about producing TV in three dimensions. The ESPN producer has captured the undulating greens of Augusta National and the flying motor bikes of the X-Games for ESPN's 3-D channel. But he can only guess how well his shows resonate with viewers. That's because 3-D audiences are so small they can't be measured by Nielsen's rating system.

"The feedback on The Masters was fast and furious. You could go on Twitter at any moment, and there'd be comments coming in every minute about 3-D coverage," said Orlins while giving a tour of a production truck at this summer's X-Games. "But then you go to some other events where it's pretty quiet."

Orlins' problem is that fewer than 115,000 American homes are tuned into 3-D channels at any one time. That's less than a hundredth of the 20.2 million-strong audience that saw television's highest-rated show "NCIS" this week. 3-D viewership is so tiny that The Nielsen Co.'s methods are unable to capture any meaningful data about viewers' programming preferences.

ESPN 3D is one of nine 3-D channels that launched in the years following the late 2009 release of James Cameron's "Avatar." The 3-D blockbuster won three Oscars and ranks as the highest-grossing film of all time, garnering $2.8 billion at the global box office.

"Avatar" was supposed to change everything. Enthusiastic television executives expected the movie to spur 3-D's transition to American living rooms, boosting sales of new TVs and giving people a reason to pay more for 3-D channels.

That never happened.

Only 2 percent of TVs in the U.S. are able to show 3-D programming, according to the most recent data from research firm IHS Screen Digest. That's about 6.9 million sets out of 331 million. After this year's Christmas buying rush, IHS expects the number of 3-D-capable televisions installed in homes to jump to 19.3 million, mostly because 3-D viewing technology is being built into most new large-screen TVs. But even with the jump, 3-D TVs will amount to less than 6 percent of all sets.

"We've learned with every passing day that we were ahead of the curve further than we thought we were," said Bryan Burns, the business leader for ESPN 3D. "We hit the on-ramp earlier than we realized at the time."

Why 3-D television hasn't become a national craze is a mystery to some in the industry, considering the wide acceptance of 3-D movies at theaters. But 3-D content is expensive to produce, and as a result there's not a lot of it. Some of the content isn't very good. Some people find the special glasses required for 3-D TV uncomfortable. And many wonder whether it's worth the extra cost.

Today, the average 42-inch 3-D television costs about $900, according to IHS.