Current TV, the ratings-challenged cable network started by former Vice President Al Gore, has put itself up for sale, The Post has learned.

“Current has been approached many times by media companies interested in acquiring our company,” CEO Joel Hyatt told The Post. “This year alone, we have had three inquiries. As a consequence, we thought it might be useful to engage expertise to help us evaluate our strategic options.”

Current is still interviewing investment banks and has yet to launch a formal sales process, said one source.

The service, launched in August 2005 after Gore had begun his crusade against global warming, has churned through programming and personnel as it tried to find its voice.

The channel started out as youth-centric and user-generated before going heavier on news and documentaries. Its latest incarnation is as a left-leaning cable news network, à la MSNBC.

In January 2011, it hired former “Countdown” anchor Keith Olbermann, after MSNBC canceled his contract. Then in March, Current also cut Olbermann loose.

The network now airs such shows as “Joy Behar: Say Anything!” and “Viewpoint with Eliot Spitzer.”

Current, owned by Gore, Hyatt and some private backers, is in about 60 million homes, which could make it valuable to buyers looking for cable network distribution.

It gets about 12 cents a subscriber from pay-TV operators that carry it, or around $82 million last year, according to SNL Kagan. Ad revenue last year was estimated at just $16.9 million.