Experience



Experience points were added to Minecraft during the first part of the Adventure Update. They were originally revealed by Jeb during an interview. Experience can be obtained by gathering Experience Orbs from defeated mobs and players.

History
Jeb has stated on Twitter that Experience Orbs will not drop unless the creature is killed by a player, rendering grinders useless for farming experience (although grinders can be converted to funnel monsters to an easily player kill-able location to grind experience). Jeb released a picture of the 1.8 GUI list, which shows the experience bar, among other things.

As of Beta 1.8, there is no measurable benefit to gaining Experience Orbs and levels.

As of 1.9 prerelease 3, experience levels are indicated by a number above the experience bar, which increases by one every time the bar is filled.

The ability to spend experience levels for Enchanting items was added in 1.9 Pre-release 3, but had no actual effect until 1.9 Pre-release 4.

Experience Level and Skill Points
Gathering experience points increases the player's experience level by gradually filling a bar on the bottom of the screen until a new level is achieved when the bar is full. Each level up will potentially reward the player with Skill Points, which Notch has said may be used for buying things such as increased jump height and increased maximum health.

Advancing from Level 0 to Level 1 requires 10 experience. An additional 20 experience is required to advance to Level 2 for a total of 30 experience. Level 3 costs an additional 30, for a total of 60, and so on. To advance from level n-1 to level n, you need an additional 10n experience. The total experience required to reach level n is 5(n*n+n).

Trivia

 * In Beta 1.8 Pre-release 1, when the player died, they dropped all of their experience orbs individually. This created a problem with retrieval of drops if the player had accumulated a large sum of experience, due to the extremely large amount of orb items created at the specific point. On SMP servers, this could be enough to even crash a server.
 * In Beta 1.9 Pre-release 1, the player gained Experience from jumping. This was part of code left in by Jeb for testing Experience.
 * Mobs do not drop experience when killed by fire.
 * Experience levels seem to get progressively harder to achieve, as experience orbs seem to fill up less of the bar the higher your level is.
 * Experience orbs will drop from a mob if it dies from fall damage as a result of the player knocking it off a cliff.

Bugs

 * When you open a 1.9 Pre Release 2 world on a 1.9 Pre Release 3 version of Minecraft, it will cause to you to have a lot of experience and cause a bug on the skill bar. Skillbarbug.png
 * In Beta 1.9 Pre-release 4, in areas where there is no light, experience orbs appear black
 * In Beta 1.9 Pre-release 4, Enchanting only consumes actual levels, not the XP itself. So if you spend 10 points on an enchantment and die you may pick up the orbs you dropped to gain the points back.