This article is about a mod.
Valve Corporation originally had plans to port Half-Life: Opposing Force into the Source engine (announced at E3 2004) much like they did with Half-Life: Source, but after seeing the results of the port the Operation Black Mesa devteam decided that it wouldn't be worth the wait, and thus took the task into their own hands. They began in September 2007, one month before the release of Half-Life 2: Episode Two.
On December 4, 2008, the old forum website was shut down due to hackers. According to the project leader, they were not aware of the team member that had assisted in the hack.
On November 2, 2009, the team released a huge media update to celebrate the 10th Anniversary of the release of the original game. Also, the project leader announced they hired new members to help with the project.
On May 1, 2012, the team released more media of screenshots along with the Guard Duty for the second update after the merge.
On August 21, 2012, they announced the Multi-player section in the original game to invitation for every fan that like to participated their meeting event to discuss how to improve both projects into much better respective view. Also, the team released both the model of RPG and Automatic-Turret for the update. .
On December 8, 2012, they release the fourth update media after the merge following the event of MOD of the year 2012. 
On February 17, 2013, the team announced the Greenlight for both projects to be on Steam after the development is finish. At the same time, they release more screenshot and concept art for the projects. .
On March 23, 2013, they released an update the first part of media for the month. .
On April 1, 2013, they released more media for the second part of the Greenlight update and announced the trailer for the near future. .
On May 17, 2013, they released the third and final part of the concluded Greenlight media update. 
On July 29, 2013, they announced that Operation Black Mesa was Greenlit and is awaiting the decision to be on Steam. At the same time, they updated the media to keep on the pact and the release date for the Beta Multi-Player for Project. .
On December 20, 2013, they thanked every fan for voting in the event of MOD of the year 2013. At the same time, the team released another update version of "We Are Pulling Out" screenshot. 
On March 26, 2014, they update another media update and announced that the Beta Multi-Player has been cancelled. 
A list of features planned for the final release:
- Complete re-creation of all twelve chapters from the original game.
- Models that push the limits of the Source engine.
- Multiplayer, including Deathmatch and Team Deathmatch with all the original levels fleshed out. A "capture the flag" mode may be included, but not in early releases.
- New voices, sounds, and visuals.
- Level design tweaks to utilize the advanced physics engine introduced in Counter Strike: Global Offensive.
- A remixed soundtrack including enhanced music from the original along with new tracks.
- New scripted scenes.
- Mod DB – Top Unreleased Mod for 2007 (5th place)
- Mod DB – Honorable mention for Top Unreleased Mod for 2009
- Mod DB - Mod of the year 2010 - Players Choice (3rd Place)
- Mod DB - Honourable mention of Top Unreleased Mod of 2011 
- Mod DB - Best upcoming Mod of 2013 (1st Place) 
- ↑ http://lambdageneration.com/posts/operation-black-mesa-and-guard-duty-the-two-gearbox-expansion-remakes-join-forces-and-merge-into-one-team/
- ↑ Tripminestudios forums
- ↑ http://www.moddb.com/mods/operation-black-mesa/news/project-relaunched-new-leader
- ↑ http://www.moddb.com/mods/operation-black-mesa/news/unforseen-consequences1
- ↑ http://www.moddb.com/mods/operation-black-mesa/news/ten-years-of-opposing-force
- ↑ http://www.planetphillip.com/posts/operation-black-mesa-and-guard-duty-interview/
- ↑ http://www.moddb.com/mods/operation-black-mesa/news/operation-black-mesa-and-guard-duty-update
- ↑ http://www.moddb.com/mods/operation-black-mesa/news/report-for-duty
- ↑ http://www.moddb.com/mods/operation-black-mesa/news/guard-duty-and-operation-black-mesa-moty-update
- ↑ http://www.moddb.com/mods/operation-black-mesa/news/greenlight-incoming
- ↑ http://tripminestudios.com/forum/showthread.php?tid=39
- ↑ http://tripminestudios.com/forum/showthread.php?tid=107
- ↑ http://www.moddb.com/mods/operation-black-mesa/news/greenlight-report
- ↑ http://www.moddb.com/mods/operation-black-mesa/news/operation-black-mesa-has-been-greenlit
- ↑ http://www.moddb.com/mods/operation-black-mesa/news/operation-thank-you
- ↑ http://tripminestudios.com/forum/showthread.php?tid=392
- ↑ Mod DB Top Unreleased Mod for 2007
- ↑ Honorable mention at the Mod DB Top Unreleased Mod for 2009
- ↑ http://www.moddb.com/events/2010-mod-of-the-year-awards/features/players-choice-upcoming-modification-2010
- ↑ http://www.moddb.com/events/2011-mod-of-the-year-awards/top100
- ↑ http://www.moddb.com/mods/operation-black-mesa/features/best-upcoming-mod-of-2013-players-choice
- Official website (Studio website)