Speech

Speech is a Fallout, Fallout 2, Fallout 3 and Fallout: New Vegas skill. In Van Buren, it was to be divided into two skills - Persuasion and Deception. The skill was also to appear in Fallout Tactics but was cut from the final game build.

The speech skill is an often used plot device at the end of Fallout games, almost always as a device to persuade the final 'boss' of the game to leave without fighting (in the case of Augustus Autumn and Legate Lanius) or commit suicide (in the case of the Master and General Jingwei).

Fallout and Fallout 2

 * $$\text{Initial level}=25+(2\times\text{Charisma})$$

Example: A starting Charisma of 5.
 * $$25+(2\times5)=35\%$$

The Speech skill was in the first draft of Fallout Tactics skills, but was eventually left out.

Fallout 3

 * $$\text{Initial level}=2+(2\times\text{Charisma})+\left\lceil\frac{\text{Luck}}{2}\right\rceil$$

Example: A starting Charisma of 5 and Luck of 5.
 * $$2+(2\times5)+\left\lceil\frac{5}{2}\right\rceil=15$$

During dialog with characters, you may be presented with a Speech Challenge. A Speech Challenge is a response preceded by the word "[Speech XXX%]", 'XXX' being the percentage chance of success (e.g. [Speech 25%]). Speech Challenges open up additional possibilities in dialog with characters, such as getting them to reveal information they would otherwise keep hidden or pay larger sums of bottle caps for a task. Not every Speech Challenge will have the same chance of success, since some characters may be harder to persuade than others. If failed, a Speech Challenge cannot be repeated.

The percentage of success is determined by various factors. The primary factor is your Speech skill. The higher it is, the better the chance of success. Charisma itself has an affect on your percentage of success. A character with a 1 in Charisma and 100 in Speech will be less effective than one with a 10 in Charisma and a similar Speech level. Having a weapon drawn will have a slight effect on your possibility of success. Finally, succeeding in a Speech Challenge with a character will make future Speech Challenges with that character easier to pass, if applicable.

Certain Speech Challenges are not checked against your Speech skill, but against other factors. These can include your S.P.E.C.I.A.L. statistics, certain perks (Lady Killer/Black Widow, Child at Heart, etc.), or your Karma. In these cases, "[Speech]" will be replaced with the relevant item being checked against ([Strength], [Karma], [Toughness], etc.). Such checks will occasionally override normal Speech Challenges. Note that these options, unlike a Speech check, will automatically succeed since you have met the requirement. Karma is an exception, as being evil or good will influence the response.

Speech success chance
The precise chance of success appears to be Charisma Bonus * Speech Skill / Difficulty, where "difficulty" depends on the particular Speech Check, but not on game difficulty level. Thus, doubling your Speech skill doubles your chance of success, and Charisma gives a non-linear bonus according to this table:

Sample difficulties for early Speech Checks are 215 to convince Lucas Simms to increase your reward, 147 to convince Gob to give you information, and 111 to convince Jericho to talk to you. Thus a 5 Charisma, 50 Speech character has a 66 base ability, and has a 31%, 45%, and 60% chance with these checks respectively. Having a weapon raised increases the difficulty by about 10%, so with a weapon up the chances would be 28%, 41%, and 54%.

Lucas Simms is actually a fairly hard sell; few Speech Checks are harder than about 170. The hardest Speech Check in the game involves the AntAgonizer, and is about 420.

Strategy
In addition to counting towards the Silver-Tongued Devil achievement, successful Speech Challenges in Fallout 3 can yield the player any number of benefits though experience is always rewarded for a successful speech check and is influenced by Well Rested status and the Swift Learner perk. Other rewards may include: a significant increase in caps for completing quests, keys or passwords, karma, additional items, or even the chance to peacefully resolve some quests without the need for violence.

Unlike Barter (which will affect a great many transactions in the game), Speech skill will only affect specific dialogue options for the non-player character's that present speech challenges in the game. Putting a large number of skill points into Speech, or selecting it as a Tag Skill assures that your character will be very, very adept with a fairly uncommon occurrence in the game mechanics.

With speech challenges, you only have one chance. Since even a high Speech skill will not guarantee success on harder speech challenges (it will guarantee it on easier challenges however as long as 100% is displayed), if you're serious about succeeding in a speech challenge, you're probably going to be careful enough to save the game before rolling the dice anyway. Using this strategy, a higher speech skill will only increase your probability of success, which translates to fewer game reloads until you succeed. Considering this, spending ten points to increase from a Speech of 30 to a Speech of 40 is likely to be completely unnoticeable in actual practice.

It is not difficult to save the game right before initiating dialogue with most non-player characters in the game. In circumstances where a non-player character will initiate conversations with you that can include speech challenges (such as Bryan Wilks, Lug-Nut, or Goalie Ledoux), these non-player characters will only appear under predictable circumstances (nearing Grayditch, obtaining the naughty nightwear, or arriving at the Red Racer Factory); thus, saving the game just before encountering these non-player characters will allow you to use the same strategy listed above. For non-player characters who can present multiple Speech Challenges—such as Bryan Wilks or Vance -- it is possible to choose the option to stop speaking to them after succeeding in the first Speech Challenge, save the game, and then talk to them again to attempt the second Speech Challenge.

Ways to increase Speech
Note: Only items adding +5 or more are included.
 * Permanent
 * Leveling up (10+INT (+3 with Educated perk))
 * Bobblehead - Speech (+10)
 * Lying, Congressional Style (+1 or +2 with Comprehension)
 * Paradise Lost (+1 or +2 with Comprehension)
 * Survival Expert (+2, 4 or 6)
 * Scoundrel (+5 with each rank)
 * Tag! (+15)
 * Yew's bear charm (+10)
 * Temporary
 * Impartial Mediation (+30 with neutral Karma)
 * Ant queen pheromones (+2-6 depending on current Charisma, a perfect Charisma of 10 will see no benefit.)
 * Grape Mentats (+2-10 depending on current Charisma, a perfect Charisma of 10 will see no benefit.)
 * Pre-War businesswear (+5, includes "Dirty" and "Grimy")
 * Naughty nightwear (+10)
 * Button's wig (+10)
 * Lincoln's hat (+5)
 * General Chase's overcoat (+5)
 * Paulson's outfit (+5)

Fallout: New Vegas

 * $$\text{Initial level}=2+(2\times\text{Charisma})+\left\lceil\frac{\text{Luck}}{2}\right\rceil$$

Example: A starting Charisma of 5 and Luck of 5.
 * $$2+(2\times5)+\left\lceil\frac{5}{2}\right\rceil=15$$

Speech no longer has a '%' chance of working as in Fallout 3. It now works 100% of the time if you have the right speech skill, which makes it impossible to save and load to bypass speech challenges. An speech challenge beyond the player's ability will usually have one dialogue option, and another when it is within the player's ability. Speech is an extremely useful skill in New Vegas, since it can frequently allow the player to avoid fights or accomplish quests more easily.

Speech in quests and exploration

 * 15, 30 and 45 Speech in lieu of Benny's evidence to convince Swank to give you your weapons back at The Tops for the confrontation with Benny.
 * 20 Speech to get Joe Cobb to tell you what he did to land himself in prison.
 * 25 Speech to convince Trudy to join the fight in Ghost Town Gunfight.
 * 25 Speech to convince Chet to supply you for the fight with the powder gangers in Run Goodsprings Run.
 * 25, 50 and 75 Speech to trick Karl into losing his cool in front of Papa Khan during the quest Oh My Papa.
 * 25 Speech to convince Deputy Beagle in Primm to stay and fight with you after you release him.
 * 25 Speech to convince Angela Williams to tell the character her opinion about Thomas Hildern.
 * 25 Speech to convince Private Ortega to tell you about the "ungrateful" farmers at the NCR Sharecropper Farms.
 * 30 Speech or 30 Medicine to convince Doc Mitchell to give you three stimpaks before initially leaving his house. Passing both will result in five stimpaks rather than six, Speech will always be the second choice (worth 2).
 * 30 Speech to convince Chavez to move on in I Fought the Law.
 * 30 Speech to convince Comm Officer Lenk to share her story.
 * 30 Speech or 6 Intelligence to convince the suspicious merchant at Jean Sky Diving to reveal himself for I Fought the Law.
 * 30 Speech to convince Johnson Nash to give up information for I Fought the Law for free.
 * 30 Speech or pay 200 caps to convince Major Knight at the Mojave Outpost to pardon Meyers for the quest My Kind of Town.
 * 30 Speech to convince Mick to sell you weapons at Mick and Ralph's.
 * 35 Speech to convince Milo to start the mission Back in Your Own Backyard.
 * 35 Speech to convince Haggerty to allow you into HELIOS One.
 * 40 Speech to convince Deputy Beagle in Primm to give you the information before you release him.
 * 40 Speech to convince each of the Misfits to be more of a "team player" in Flags of Our Foul-Ups.
 * 40 Speech to convince Jane in Freeside to give something else of value towards her debt in quest Debt Collector.
 * 40 Speech to convince Thomas Hildern to improve the offered reward in There Stands the Grass. (available after talking to Dr. Williams and returning to confront Hildern)
 * 41 Speech to convince Boone to tell you who he's on the lookout for.
 * 45 Speech to convince Jessup to release the hostages in Boulder City.
 * 50 Speech to convince Neil to help you kill Tabitha in Crazy, Crazy, Crazy.
 * 50 Speech to convince Tomas to get rid of his necklace.
 * 50 Speech to convince Joana you have what it takes to have sex with her, which follows into another speech challenge of 75 in order for her to lead you to her room and commit the deed.
 * 50 Speech or the Black Widow perk to convince Chris Haversam that he's human in Come Fly With Me.
 * 50 Speech to obtain thrust controllers for 250 caps from Old Lady Gibson for Come Fly With Me.
 * 50 Speech to convince Ralph to craft you a counterfeit passport for The Strip at a cost of 500 caps.
 * 50 Speech to get away with killing Caesar with the autodoc during Et Tumor, Brute? (as an alternative to 50 Medicine or positive Legion reputation)
 * 50 Speech to convince Pearl to give Janet a free pass into Nellis in Young Hearts.
 * 53 Speech to convice Big Sal to release Troike from his contract.
 * 55 Speech to get the Think tanks to realize that you are aware of their conversation.
 * 60 Speech to convince Keith to show you how he's cheating at Caravan.
 * 60 Speech to convince Pacer to let you see the King for free.
 * 60 Speech to convince Private Stone to turn himself in during the Medical Mystery quest.
 * 60 Speech to convince Benny to head immediately to The Tops presidential suite without his bodyguards.
 * 60 Speech to lie and convince Private Edwards to leave the Camp searchlight house he is holding out in by saying that all the radscorpions are gone.
 * 60 Speech to gain Jack's trust in Oh My Papa.
 * 62 Speech to convince Mortimer to choose the cannibal side in Beyond the Beef.
 * 64 Speech to convince all Fiends inside of Vault 3 so they will not attack you.
 * 65 Speech to convince the gambler to a weapons check while guarding the front of the Silver Rush during Birds of a Feather.
 * 65 Speech to convince Norton outside of Jacobstown to leave the mutants alone in the quest Unfriendly Persuasion
 * 65 Speech or 45 Medicine to convince Caesar to let you operate him in "Et Tumor, Brute?".
 * 65 Speech to ask Dog/God "Why did you put emphasis on the word "Master" before?" after freeing him from the jail. Dead Money
 * 66 Speech to convince Jack in the Red Rock Drug Lab to make medicinal chems.
 * 70 Speech to make Troike plant the thermite in the Gommorah himself in How Little We Know, giving you bad Karma.
 * 75 Speech to make Dog let God take over in the Dead Money DLC quest Put the Beast Down. (This can only be done if you convinced God to come out of the cage in the quest Find Collar 8: "Dog".
 * 75 Speech to convince the Strange Man during the Birds of a Feather quest to pay you for running chems.
 * 75 Speech or the Confirmed Bachelor perk to convince Arcade Gannon to be your companion.
 * 75 Speech to convince Alice McLafferty to give Janet her wages.
 * 75 Speech to cause Tabitha to order the nightkin under her command to attack the super mutants at Black Mountain when activating a radio during Crazy, Crazy, Crazy.
 * 80 Speech to convince Keene for not taking the Stealth Boy Mk2 in the quest Guess Who I Saw Today.
 * 80 Speech to convince Isaac that the Gun Runners can use refurbished weapons while Dealing with Contreras.
 * 80 Speech to convince Orion Moreno to stay with the Remnants and fight for the NCR during the quest For Auld Lang Syne.
 * 80 Speech or good Karma to convince Legate Lanius to fight you one-on-one.
 * 80 Speech in order to convince Hector to tell you what he knows about Corporal White during the quest The White Wash.
 * 80 Speech to convince Cachino to take care of Big Sal and Nero in How Little We Know.
 * 80 Speech to lie to Troike about telling the NCR of his dealing in the Gommorah in How Little We Know, giving you bad karma.
 * 80 to convince Big Sal that Nero was plotting against him in How Little We Know.
 * 85 Speech to avoid combat at the conclusion of Bye Bye Love by convincing your pursuers that Joana's escape is part of a secret deal between Carlitos and the Omertas.
 * 85 Speech to say Dog/God "You want to protect Dog..." after freeing him from the jail. Dead Money
 * 85 Speech to convince Dog/God to merge personalities in the Dead Money DLC quest Put the Beast Down.
 * 95 Speech to talk your way out of combat after bringing back the objective in I Could Make You Care and then leaving the Brotherhood of Steel base.
 * 100 Speech to convince Lee Oliver to leave Hoover Dam without fighting you during the quest Veni, Vidi, Vici.
 * 100 Speech to convince Legate Lanius to leave Hoover Dam without fighting you.

Ways to increase Speech

 * Permanent
 * Leveling up (+15 or +17 with Educated)
 * Lying, Congressional Style (+3 or 4 with Comprehension)
 * Empathy Synthesizer (+2 depending on current Charisma, a perfect Charisma of 10 will see no benefit.)
 * Tag! (+15)
 * Good Natured (+5)
 * Skilled (+5)
 * Temporary
 * Meeting People (+10 or 20 with Comprehension)
 * Mentats (+2 depending on current Charisma, a perfect Charisma of 10 will see no benefit.)
 * Party Time Mentats (+2-10 depending on current Charisma, a perfect Charisma of 10 will see no benefit, can be stacked with Mentats)
 * Absinthe/Beer/Irradiated beer/Jake Juice/Scotch/Irradiated Scotch/Vodka/Whiskey/Irradiated whiskey/Wine (+2 depending on current Charisma, a perfect Charisma of 10 will see no benefit.)
 * Sexy sleepwear (+2 depending on current Charisma, a perfect Charisma of 10 will see no benefit.)
 * T-51b power armor helmet (+2 depending on current Charisma, a perfect Charisma of 10 will see no benefit.)
 * Sheriff's duster (+2 depending on current Charisma, a perfect Charisma of 10 will see no benefit.)
 * Bounty hunter duster (+2 depending on current Charisma, a perfect Charisma of 10 will see no benefit.)
 * Regulator duster (+2 depending on current Charisma, a perfect Charisma of 10 will see no benefit.)
 * Vault jumpsuit (+2)
 * Benny's suit (+5)
 * Caesar's armor (+5)
 * Dean's Tuxedo (+5)
 * President Kimball's suit (+5)
 * Pre-War businesswear (+5)
 * Vera's outfit (+5)
 * Naughty nightwear (+10)

Speech-based perks
Retoryka Красноречие