Kmart's 'Ship My Pants' video may have taken YouTube by storm, but it's the retailer's follow up -- 'Big Gas Savings' -- that's truly outperforming.

According to Advertising Benchmark Index, which measures ads' effectiveness across all media channels, Kmart's second punny ad scored well above average and performed well in all of the areas ABX measures. It's quite the coup for a brand not exactly well-known for out-of-the-box advertising.

"Getting pants or anything else shipped to you is not nearly as compelling nor universal as saving money on gas," said Gary Getto, president at ABX. "In the case of Big Gas Savings, the messaging was clear and easily understood and the humor was not quite as lewd as the Ship My Pants ad and did not generate the level of dislikes that Ship My Pants did."

Indeed, twice as many people disliked the Ship My Pants ad, according to ABX, while a larger portion of people reported they'd like to watch Big Gas Savings again. Big Gas Savings also scored higher in areas including awareness, relevance and the overall clearness of the message.

Ship My Pants launched on April 10 and quickly garnered millions of views on YouTube. To date, the ad, which began airing on TV two weeks later, has racked up more than 18 million views. Big Gas Savings launched on May 23 and has about 4 million views on YouTube.

Kmart's been mum on the subject of whether it'll continue this streak of puntastic advertising. When asked earlier this month whether there's a fear that the joke is already getting old, a Kmart spokeswoman said only: "Creativity is important in Kmart's advertising; especially to engage our members and share new information on promotions and initiatives. We believe that humor is a natural part of the strategy."

An agency change could determine the direction Kmart ultimately goes in. The retailer is in the midst of wrapping up an ad agency review it launched earlier this year. According to executives familiar with the matter, it's down to a shootout between sibling agencies DraftFCB, which is trying to defend the business, and McCann.