Currently, Global Offensive features five game modes for online play:
- Classic Casual and Competitive: Counter-Strike's most well-known game mode, both involving Bomb Scenario and Hostage Scenario missions. At the start of each round, players can purchase weapons and gear with money earned from various actions, from assisting on kills to completing objectives. Regardless of mission type, a round ends when one team completes an objective, eliminates the other team, or lets the timer run out.
- Bomb Scenario: the Terrorists must plant a C4 explosive at one of two designated bombsites; the Counter-Terrorists must prevent the bomb from exploding, either ensuring that the terrorist team does not plant it or defusing it once it is activated.
- Hostage Scenario: the Counter-Terrorists must rescue hostages from the Terrorists, and bring them to an extraction point; the Terrorists must prevent the hostages from escaping. If a Terrorist or Counter-Terrorist attempts to kill hostage, they will suffer a heavy cash penalty. An update later changed how Counter-Terrorists rescue hostages: instead of leading them around, players must carry one hostage at a time to the extraction point.
- Arms Race: a deathmatch-based mode where each player is rewarded for each kill with a new weapon, with the first player to get a kill with every weapon in a predetermined set winning the game.
- Demolition: a round-based mode that removes weapon and equipment purchasing, instead rewarding players who manage at least one kill by giving the next weapon in a predetermined set of weapons. After a second kill with that weapon the players are also rewarded a grenade (of a random type) along with their new weapon for the next round.
- Deathmatch (added on November 12, 2012): a mode consisting of 10-minute matches. Players must gain the highest possible score by earning kills with different weapons or desired weapons. The number of points from a kill depend on the weapon. Players may also take advantage of bonus timers for different weapons, using them to score extra points. Like in Arms Race, players automatically respawn after getting killed, but also when they choose to respawn with bonus weapons.
*Global Offensive also offers two offline modes: Offline with Bots, which offers the same game modes with AI-controlled bots; and a Weapons Course for inexperienced and veteran players alike.
- Online play
Global Offensive supports matchmaking and leaderboards for all online game modes, provided by Steam.The provided online service offers the ability to filter by game modes, maps and a built-in Steam friend system. Valve also employs Valve Anti-Cheat, which can automatically remove and ban players from the Valve online network. To match players of similar skill levels for an enjoyable experience, the game uses an heavily modfied version of Elo rating system. The PC version of Global Offensive also supports private dedicated servers that the player may connect to through the community server menu in-game. These servers may be heavily modified and can be completely different from the base game.
Counter-Strike: Global Offensive is the first Counter-Strike game to include a built-in competitive mode. The difference between Competitive and Casual mode were somehow significant. In Competitive mode pits a team of 5 Terrorists against 5 Counter-Terrorists in a maximum of 30 rounds match. After 15 rounds the two teams switch sides. The first team to score 16 points wins the game. If both teams score a total of 15 points by the end of the 30th round, the match will end in a tie.
Unlike the Casual game modes, the player is given the option to choose which map will be played specifically using checkboxes.
- Professional play
Competitive mode is used exclusively in professional tournaments such as ESL One tournaments, or professional gaming leagues such as CEVO. The standard competitive setup can be modified slightly to accommodate the tournament rules, such as 6 rounds overtime in the case of ties. Professional gaming is also referred to as eSports, and is closely tied to the CS:GO community. A portion of the proceeds from eSports keys go towards cash prizes in official Valve sponsored tournaments.
- Skill groups
Starting with the October 25, 2012 update, skill groups were introduced to help the player understand how the competitive matchmaking works. When entering a Competitive game, player has to play 10 games to be assigned into a specific group/rank. The matchmaking system will try to place the player with other players around the same skill level.
- Competitive matchmaking cooldown
If a player has abandoned a match, cheated, or otherwise poor sportsmanship, the player will receive a competitive matchmaking cooldown (reffers to a kind of timeout/ban). When a player has a competitive matchmaking cooldown, the player cannot participate in a competitive match for the duration of the cooldown. The player will be notified of a cooldown by receiving a yellow banner at the top of the main menu page with the remaining length of the cooldown.
- Cooldown legnths
During the cooldown period, the player cannot play any competitive matchmaking, but can still play any of the casual game modes. Cooldown levels drop by 1 level after a week with no additional offenses. If one has already reached a 4th level cooldown and gets another cooldown the level will rise, but the duration of the cooldown will not be extended. There is no known limit to how much levels a person can get.
- Reasons for a cooldown
Most of the actions triggering a cooldown occur during competitive matchamking. However, some actions outside of competitive game modes can trigger or lengthen a player's cooldown period:
- Abandoning a match - Leaving a competitive match mid-game, through direct player action or in-action. The first abandon has a 30-minute cool down, the second is 2 hours, then 24 hours, and one week. If you haven’t abandoned for a week you would cool down by one level (for example, from 24 hours back to 2 hours).
- Team disruption - activities such as teamkilling, excessive team damage, or a player being repeated vote-kicked from matches in competitive matchmaking.
- Cheating - Use of 3rd party programs, scripts, or other hacking techniques in competitive or casual matchmaking.
- Idling - Excessive idling (AFK) on competitive or casual matchmaking servers.