Why I'm not waiting for the oil bottom: Rubenstein

Time to bet on energy?
Time to bet on energy?

Carlyle Group's David Rubenstein told CNBC on Tuesday he is not waiting for oil to hit a bottom before investing in beaten-up energy companies.

"The great fortunes are usually made when prices are low. They're not usually made when you buy at the top and think they'll get higher," he said in a "Squawk Box" interview. "Prices are very low in energy, and a lot of people are scrambling, and that's where you make a lot of money."

Rubenstein has called distressed debt "the single greatest new energy opportunity to invest," saying investors can by debt cheap and potentially take control of companies.

Read MoreNext curveball for oil: An Iran nuclear deal

The Carlyle Group has about $9 billion to deploy on energy investments, Rubenstein said, adding that it is a small part of its legacy business and not very much relative to the opportunities. The private equity firm has $194 billion of assets under management.

Oil prices plunged 60 percent between June and January before stabilizing in February.

Rubenstein said he is focused on investments in carbon-related energy, particularly companies that build new infrastructure for the energy industry. He is also looking outside the United States for opportunities.

While investors might get to heaven a bit more quickly by buying into renewable energy, the returns are not yet proven, he said.

Read More Solar energy's unexpected conservative backers

"We have a lot of oil and gas that's relatively cheap compared to its replacement value, and as a result of that I think it will be one of the great areas to invest over the next five to 10 years, as it has been for many many years," he said.

Carlyle is taking a long-term view of energy, he said, noting that the firm typically holds companies for six or seven years. Within three years, he expects oil prices to rebound, but acknowledged that the market does not know how the world's top exporter, Saudi Arabia, will act in the future or how geopolitical tensions between Russia and the rest of Europe will affect the energy market.