NBC Universal has put four of its smallest NBC stations up for sale as part of a broader strategy to invest in Telemundo stations and to seek duopoly opportunities in markets where it already owns stations, according to sources.

The media company is in the early stages of the sale, which is expected to take months to complete and could fetch around $600 million, a source said. The stations up for sale include WCMH-TV in Columbus, Ohio; WJAR-TV in Providence, R.I.; WNCN-TV in Raleigh, N.C.; and WVTM-TV in Birmingham, Ala.

NBCU owns 14 NBC stations and 15 Telemundo stations. An NBCU spokeswoman declined to comment.

The auction of the four stations comes as NBCU looks to improve the distribution of its Spanish-language network Telemundo, create more duopolies of NBC and Telemundo stations and concentrate on owning stations in areas experiencing rapid Hispanic population expansion. It also comes at a time when stations are being sold at robust cash-flow multiples, as evidenced by the recent sales of Emmis Communications’ stations and all of Liberty Corp. to Raycom Media. Already NBCU has purchased a television station in Las Vegas and is involved in a swap deal for a full-power station in Phoenix for Telemundo. The company is also keen on acquiring a full-power station in Denver.