|For a cross-game overview of this skill, see Barter.|
The Barter skill is primarily used in the buying and selling of items, such as trading with a merchant or scavenger. In general, purchase prices will be lowered and selling price will be higher. It is the primary factor in price determination, and is also offset by the Barter skill of the non-player character in question. The skill is also used in certain dialogue options with non-player characters, where certain responses require Barter checks.
Like Fallout 2, the skill only affects the price for which merchants offer an item. The player character's offer prices to the merchant are always the same as the base value of the item, regardless of Barter skill level.
Barter can more effective in Fallout compared to Fallout 3 and later, due to a low number of caps located in-game. However, this is often offset by ease at which caps can be generated using the Gambling skill.
Depending the level of Barter skill, item prices may be as high as 10x the value of an object, eg. Rad-X has a base value of 300 caps but may be purchased for as much as 3,000 caps, or combat armor has a base value of 6,500 caps and may be purchased for as much as 65,000 caps. Generally, the higher the Barter skill, the lower the purchase price will be.
Ways to modify Barter
- Gifted trait: -10% to all skills
- Good Natured trait: +15% to all skills
- Tagging Barter skill (at character creation or with Tag! perk): +20% Barter skill
- Leveling up: +1/+2% for each non-tagged/tagged skill per skill point assigned
- Master Trader perk: +25% Barter skill, hidden 
- Singing with Patrick the Celt: +1 Charisma (up to +2% Barter skill)
- Consuming a dose of Mentats:
- 0–24 hours after dose: +1 Charisma per dose (up to +2% Barter skill per dose)
- 24–96 hours after dose: -2 Charisma per dose (up to -4% Barter skill per dose)
- Other modifiers
- Difficulty Level: +20/+0/-10% to non-weapon skills for Easy/Normal/Hard difficulty
- Reputation (aka. Karma for Fallout): -25/+0/+50% to Barter skill for Bad/Neutral/Good reputation, hidden 
Like Fallout, the skill only affects the prices for the vendor's items; the player character's items are always worth the same.
The initial level for Barter is still governed by Charisma, but usually starts out lower than Barter in Fallout.
Barter also determines how much things can be sold for in Tactics, whereas selling prices were always static in the previous Fallout games.