In preparation for the launch of the Stygian Abyss expansion, support for the existing client was discontinued to optimize the patching procedure.

The release of Trammel led the developers to distinguish the original world by making the environment more grim and naming it "Felucca".

Garriott commented that "it was very important to us that Ultima Online be a game with a theme, and story, and quest - and then support larger, grander activity.

[15] The initial team was composed of Garriott, Starr Long, Rick Delashmit, Scott Phillips and, a bit later, Raph Koster, who became the lead designer.

[18] The development cost was much greater than for previous, offline computer games; it relied on people accessing servers via modem.

Ultima Online's initial features included persistent player housing, skill-based character progression (without levels or classes),[19] a craft-based and player-driven economy,[20] and unrestricted player-versus-player combat.

A preview announced that ecological events in the game would affect animal behavior, potentially creating new adventure possibilities in an organic manner.

During a server population stress test, a player character known as Rainz cast the "fire field" spell, killing Lord British.

[27] Upon release, Ultima Online proved popular, reaching 100,000 paying subscribers within six months, causing severe lag problems.

In February 2000, a large in-world event had a massive army of undead lay siege to the Britannia city of Trinsic.

In November 2000, Ultima Online's first official fanfest was held, called the UO World Faire in Austin, TX.

[31] This may in part be attributed to the 2004 release of World of Warcraft, which quickly established hegemony over the MMORPG market and has attracted scores of players from all preexisting games in the genre.

After Stygian Abyss the development model shifted from expansions to "booster packs" that were intended to be smaller updates released more frequently.

[33] In 2020, Broadsword announced a new shard that would focus on returning Ultima Online to its fundamental roots as a roleplaying game.

[43] In the United States, Ultima Online debuted at #9 on PC Data's computer game sales rankings for October 1997.

[45] A writer for CNET Gamecenter found that the title was part of a trend of role-playing successes in October, alongside Fallout and Lands of Lore 2: Guardians of Destiny.

A writer for PC Gamer US considered this speed the possible cause for "the many reports of lost orders, delayed pre-orders and stores out of stock that occurred when the game launched.

"[48] In mid-November, Electronic Arts revealed plans to ship an additional 80,000 units of Ultima Online worldwide, including 15,000 for Japan.

[46] The game had fallen from PC Data's monthly top 20 for the United States during November,[50] but the firm tracked 87,000 sales of Ultima Online in that country alone through the end of 1997.

"[52] The game had risen to 120,000 subscribers by March 1999,[53] and by June Ultima Online's global sales had surpassed 200,000 units.

[55] Domestically, Ultima Online and its Second Age add-on together had sold 249,610 copies and earned revenues of $11.3 million at retail alone by early 2000, according to PC Data.

Gamecenter's Mark Asher wrote at the time, "Add in its current subscriber base of 150,000 players at $10 per month, and you can see the appeal of online, fee-based games.

[70] Since the designers of Ultima Online wanted to provide freedom and sense of agency, it was important to allow players to act in a villainous role.

Expansion packs have been released regularly, all of which add new content in the form of landmass, art, quests, items, or game mechanics.

The 3D client was originally released as a part of the Ultima Online: Third Dawn expansion, but received poor reviews due to performance issues (especially memory leaks early on) and sub-par graphics.

[79] A series of clues provided by developers via an in-game event arc allowed players to find a URL on the Ultima Online website wherein a simple message was contained as well as a Flash movie featuring screenshots of the upgraded graphics.

The new client modernized the game's look, making it easy to add new content without backsliding through outdated and outmoded art, while maintaining the niche market as an MMORPG that can run on lower-end computers.

Electronic Arts referred to the Ultima Online: Kingdom Reborn client as "2.5d," meaning that it was written in 3d and then moved into 2d to make it easier for lower-end computers to run.

Support for this client ended to streamline the patch process prior to the release of the Ultima Online: Stygian Abyss expansion.

Ultima Online has had several special releases that were not expansions or booster packs, but came with boxed or in-game extras.