Why you should buy energy stocks now: Expert

Investors should be on the lookout for energy stocks, according to Morgan Stanley (MS)'s chief market strategist. Adam Parker told CNBC's " Squawk on the Street " on Friday that the time to buy energy stocks is now. "Energy stocks are cyclical," he said. "All seven times they've gone down this much in the past, they've subsequently outperformed six months later." Read More Energy M&A may not come until 2016: Experts Investors should not wait for energy stock earnings to hit bottom to start buying energy stocks, Parker also said. "You have to be early," he said. "You have to buy them two to three months before the earnings revision bottom. You can't wait for them to bottom. [Once they bottom], the stocks are off to the races." The energy sector has been hit hard by falling oil prices. The WTI (New York Mercantile Exchange: @CL.1) and Brent (Intercontinental Exchange Europe: @LCO.1) indexes were at about $45 and $49 per barrel, respectively, Friday morning.

Read More Best ways to profit from beaten-down energy stocks Parker added that he believes energy stocks will rise because of their valuation. "If you look at price-to-book [ratio], ... historically, it's the most effective metric of predicting subsequent return in energy," he said. "The stocks are pretty cheap. You have to be buying them on a belief that oil will be higher 12-to-18 months down the line."