KOOL-FM (94.5 MHz branded Big 94.5) is a commercial classic hits radio station in Phoenix, Arizona, owned by Audacy, Inc. Big 94.5 features mostly hits of the 1970s, 1980s, and 1990s. KOOL-FM's studios are located in downtown Phoenix, and its transmitter is in South Mountain Park.

KOOL-FM began programming oldies music in 1971, the first radio station ever to carry the format, as a format brought to the station by Jerry Osborne, who used the air name Dan Coffey. Since the station did not have an oldies library, Osborne supplied all of the music from his own collection. The Dan Coffey Show, which aired on Saturday and Sunday nights, from 6:00 to midnight, immediately became the most popular program on KOOL-FM – so much so that they hired a woman (Pam MacKenzie) whose only job it was to answer the flood of calls and music requests for the Dan Coffey Show. At the time, no other station in the Phoenix market had an oldies format, and Osborne was given the freedom by KOOL-FM (then owned by Gene Autry) to play anything he wanted.

Now the door to success was opened and by the end of 1971, the entire station followed. They switched to an all-oldies format. In 1975, Osborne left radio to start his own publishing company. Before he left, he recorded thousands of oldies for the KOOL-FM music library.

By about 1986, KOOL was playing a small amount of 1980s music as well. Still, they focused on the music of the late 1960s. More often, KOOL's schedule then was unique, despite the station airing mostly oldies, but KOOL aired Rick Dees Weekly Top 40 for a short time during early and the middle of 1984. The show was dropped that August due to low ratings according to The Arizona Republic. The station was co-owned with KOOL/960. In December 1985, Adams Radio Group bought both KOOL-AM/FM from Tom Chauncey and Partners. As Adams radio took ownership, KOOL-AM under the tutelage of GM Jim Seemiller changed format to a 1950s/1960s early rock and roll oldies format on January 7, 1987. The music had a concentration of the early hits but also injected a large dose of doo-wop. This new format caught on and not only became a ratings success but also syndicated itself 24 hours a day, the first radio station to do so. The stations were both owned by Adams Communications, and KOOL format was installed at many of other Adams radio stations.

KOOL with its marketing savvy became the leader of oldies in the US. KOOL had its own Radio store, a physical shop located in Phoenix with radio paraphernalia, records, music, and other oldies items and had a tremendous retail operation. At the same time, KOOL opened its own version of a real bar, KOOL CAFE. With the Cafe KOOL did music and live promotions every day of the week. The Cafe became one of Phoenix's hot spots for years. These marketing tactics paid off with the winning of the Marconi award in 1991/92.

In late 1995, KOOL-FM began simulcasting on KOOL-AM, which stopped playing "older-leaning oldies".

In 1996, Chancellor acquired KOOL-AM-FM. At that time they acquired several other stations in the market, bringing them over their ownership limit of 8. They opted to sell KOOL-AM-FM to Salem Media in 1997 and the AM, renamed KPXQ, became a Christian Talk station. In 2002, KPXQ became NewsTalk 960 KKNT focusing on conservative talk radio.

KOOL-FM went to Infinity Broadcasting, later to become CBS Radio. The music continued to be about the same until about 1999. At that point more late 1970s songs were added while the pre-1964 oldies were cut back slightly. In 2001, some early 1980s music was added and the pre-1964 oldies were cut to about two per hour. By 2003, as was the case as the oldies format continued to evolve, the pre-1964 oldies were eliminated almost completely with a handful of exceptions. More 1980s titles were also added at that point. Today the station, like most oldies outlets, has more of a classic hits format than a true oldies format.