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Plunging oil prices may be rough for energy companies, but they're a tail wind for the U.S. economy, billionaire value investor Mario Gabelli told CNBC on Tuesday.

In a "Squawk Box" interview, Gabelli, founder, chairman, and CEO of Gamco Investors, cited two industries that he's betting on because of lower oil and gasoline prices: They're auto parts and convenience stores.

He likes distributor Genuine Parts and auto parts retailers O'Reilly Automotive and AutoZone.

"The users of energy, the owners of the cars are feeling better, so that they buy parts at AutoZone, O'Reilly's [and] Genuine Parts. Those businesses are doing quite well," Gabelli contended. "They benefit because there are 250 million cars are on the road. There's deferred maintenance."

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Auto parts stocks

Those three stocks have also been performing solidly this year. As of Monday's close, AutoZone is up 28 percent in 2014, Genuine Parts is up 24 percent and O'Reilly Automotive is up 47 percent.

Another company in the auto part space, Pep Boys, has not been executing well and its stock is off 27 percent this year, he said.

Convenience store stocks

As for convenience stores, Gabelli said he likes Murphy USA and Casey's General Stores based on lower oil prices as consumers start feeling better about filling up their tanks. Shares of Murphy and Casey's are up 46 percent and 17 percent, respectively, for 2014 as of Monday's close.

"Every week you're going to feel better. But you don't do it right away. Seventy percent of gasoline purchases are with debit cards or credit cards. And it's going to take about a month when you're bill is lower and you got more money leftover."

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Media stocks

In the media space, where Gabelli is also heavily invested, he believes that CBS should buy Viacom, the company behind MTV and Paramount Pictures. "Someone is going to try to put the two together. They make sense to come back together." The two media giants split into separate companies at the end of 2005, with the two stocks trading separately as of Jan. 3, 2006.

Viacom is down 15 percent so far this year, while CBS is off 18 percent in 2014 as of Monday's close.

At an investor conference on Monday, which Gabelli attended, Viacom stressed the importance of the global marketplace for media consumption, "the notion of a smartphone, watch what you want, where you want to watch," as the Gamco Investors boss put it.

Gabelli also pointed to Viacom's buy back of $2.5 billion in stock this year as a positive. "I'm increasing my ownership of the company for my clients," while keeping the number of Viacom shares owned constant.

Disclosure: According to the 13F filing from Gamco Investors at the end of September, the investment company owns shares in all the stocks mentioned in this article.