Extended play 45s were an attempt to get more songs on the standard 45. They typically had two songs on each side and came with a stiff cardboard cover, making them look like a miniature version of a normal LP. In 1953, when the EPs were introduced, the LPs introduced at the same time were the 10-inch discs with four songs on each side. The EP was therefore equivalent to half of one of these albums, and a two-EP set in a fold-open cover was the equivalent of a 10-inch album. When the 12-inch LP disc began to become popular in the mid-1950s, the EP was reduced to a one-third equivalent of the LP, so three-EP sets were issued to correspond to the (then-standard) 12-inch LP. For all intents and purposes, the multiple-EP "album" was discontinued in 1956, being a poor seller relative to the 12-inch 33-1/3 rpm discs.

EP albums, which were introduced in 1953 with X207, first used the X-1 series, which had started in 1950 and was the counterpart to the E-1 (10-inch LP) and K-1 (45 album) series. The X-1 EP albums essentially corresponded to the 10-inch LP series. When 10-inch LPs were discontinued in late 1955, the numbering system for EP albums continued with the 12-inch LP series catalog numbers (E3000 series). In each case, while the LP had an "E" prefix, the EP album had an "X" prefix.

We would appreciate any additions or corrections to this discography. Just send them to us via e-mail. Both Sides Now Publications is an information web page. We are not a catalog, nor can we provide the records listed below. We have no association with MGM Records or Universal Music Group, who currently own the masters. Should you be interested in acquiring albums listed in this discography (which are all out of print), we suggest you see our Frequently Asked Questions page and follow the instructions found there. This story and discography are copyright 2000 by Mike Callahan.